Some points to add...

E7 storage heaters.
E7 storage heater generally suffer low retention, that is up to 60% of
heat is convected
out overnight with a mere 40% of heat retained to maintain temperature
through the subsequent
evening before the next charge period. The wrong solution is to
oversize the heater in order
to retain sufficient heat by evening - it will, but you will barbecue
from about 4am onwards
as the heater top damper opens full bore. Equally wrong is undersizing
- they will be cold &
useless, relying excessively on peak-rate electricity to compensate.

Conventional E7 storage heaters are of little use a) if you are out
working during the day
(ie, not a pensioner) as their heat diminishes by the time you return
or b) poorly insulated.

E7 storage heating is about getting as much insulation as possible
before hand: 200mm+ of loft
insulation, cavity wall insulation (CWI) and all glazing/door sales in
good working order. Check
even if you have CWI whether any walls are solid, often bathroom or
corner room walls are,
anything over a porch or entry, or even all the upstairs in older
houses. Double glazing is
obviously good, but the payback period is so long (up to 164 years) it
can be better to tackle
other alternatives first. Double glazing saves 50% of the heatloss
through your windows, not
50% of your overall heatloss if you do not already have loft & CWI
insulation.

An improvement to conventional E7 storage heater is to use E10, an
afternoon-boost tariff.
This typically gives 3 charge periods bringing the heater & house back
up to temperature.
Unfortunately a special tariff can hold you hostage to an insufficient
number of suppliers
to achieve price competition - either now or in the future. This is
particularly the case
with non-storage electric heating where claims are often entirely
dependent on such tariffs.

Improved E7 storage heaters, such as Dimplex Duoheat & Creda Eco, use
a peak-rate boost element.
These work on the basis that the heater core even when appearing cool
still has the ability to
heat air some way above ambient, so requires only a small supplemental
element (eg, 0.29-0.39kW)
to boost the heater casing temperature to a meaningful delta above
ambient. Whilst they work if
1) insulation is satisfactory 2) they are sized adequately.
Undersizing in output or number will
result in excessive use of peak rate electricity, their maximum output
is 2.55kW rather than 3.3kW
of conventional units often necessitating 2 units which greatly
increases cost (2x £380 vs 1x £420).
Additionally they add complexity which could impact on reliability -
unknown 10yr+ availability of
PCB electronics & thin-film elements compared to conventional storage
heater which is simply a
box of "resistor elements + bricks + capillary electromechanical
thermostat" for 25yr+ life. It is
said that conventional storage heaters do not fail, they are buried
with the previous occupiers.

E7 storage heaters of the slimline variety can also be had with a fan,
which seems of dubious use
since the design is a high convective type so the fan will merely
extract more heat from the core faster.
The fan is best used with peak-rate element to avoid heat
stratification that otherwise can occur.

A significant improvement to conventional E7 storage heaters is to use
commercial units.
Commercial E7 storage heaters have vastly higher retention rates, 40%
of heat some 17hrs after E7 has finished,
which allows them to be sized to avoid the overnight roasting & cold
subsequent evening. This is achieved by
increased use of silica block & no top venting core damper opening
part way through the charge period.
Instead a fan extracts heat as required on-demand via a case mounted
or wall mounted thermostat dial.
Whilst this partly solves the problem of "house roasted by convection
oven" it comes at a stiff penalty
in terms of size (typically 285mm deep) and price (typically £800-1400
a unit). So just 2 heaters cost
the same as a high-end combi installed.

In summary E7 storage heating can work, but it relies on careful
sizing & substantial levels of insulation.
Even then the commercial solutions are not particularly good, just
better than bad. The fan is a failure point,


Electric wet / hydrionic heating.
This may be the migration step someday if UK gets sufficient nukes,
but probably not as currently envisaged.
Any electric wet heating must 1) use an afternoon-boost tariff like
E10 or b) very large thermal store heated up on E7.
Unfortunately many systems (particularly in flats) are not on the
right tariff (or not programmed to match the tariff)
and do not have an adequately sized thermal store which is "charged"
during off-peak pricing. The effect is massive bills
and they can even be unresponsive if wet radiators are high water
content (fast warmup). To heat a typical semi on an E7
thermal store would be quite a challenge, I suspect 3-4x 250L tanks
with 4" of rockwool insulation. E7 is about 5p/unit
& peakrate 12p/unit as of 2008, with gas around 3.85p/unit plus
adjustment for efficiency ((65)-82-91%) plus adjustment
for annual servicing plus adjustment for depreciation (ie, a new
boiler fitted is £3500 every 10yrs, more often if a
bargain basement combi is used in the south with basic aluminium heat
exchanger rather than stainless steel).

A more likely migration step is a heating system utilising heat pump
technology - air/ground to water.

Air to air heat pumps.
Units from Fujitsu in particular can achieve 2.5 CoP down to -10oC, a
temperature that is rarely seen in the UK
and very unlikely during the day. Typically a bad January period is
-1oC during the day, -5oC overnight. That 2.5
CoP translates into 2.5kW out for 1.0kW in - that 1kW even at peak
rate is thus reduced below even gas prices.
The counter is a heatpump may have a life of 3yrs (DIY install, poor
seals) to 10yrs so either factor in an
annual maintenance or depreciation for capital replacement. Lifetime
cost directly drives up the real kW cost.

The key barrier to air sourced heat pumps is often noise - whether
planning permission is required is unclear
in many situations, boundaries can be very close and noise pollution
is severely frowned upon. Outdoor units
can range from 46-58dB(A) which is quite a substantial figure - not on
a par with a Dyson, but not silent either.

Supplementary heating is therefore potentially required at periods
below -10oC.
However Canada to Sweden routinely adopts heatpump technology in
temperatures below that of the UK successfully,
the problem is not the real-world CoP with modern invertor units but
the noise w.r.t. neighbours who may complain.

Ground to air heat pumps.
Ground to air heat pumps have two benefits over those sourcing from
the air a) the ground at 1.5m is around 9oC
all year round b) there is no noisy fan stuck on your outside wall.
CoP can be somewhat better, 2.8-3.2 however
the problem is the nature of the ground - extracting "heat" from the
ground requires its replacement. Ideally the
ground should be a wet clay rather than a dry chalky area to ensure
CoP remains high rather than deteriorates.
Unsurprisingly the best CoP comes from clay hillside locations or
those with access to a nearby spring.

Air/Ground to Water heat pumps.
These seem attractive by virtue of their ability to replace existing
gas boilers. Unfortunately the water output
temperature is restricted - a very high temperature results in very
low CoP, a very low temperature results in a very high CoP.
Radiators require oversizing (doubling ideally) and DHW requires a
boost element (E7 would be ideal). In essence they are
best served feeding a wet thermal store, permitting a smaller thermal
store to be adopting than would ever be possible
with a purely E7 resistance heating solution. A heat store does also
permit the winter day/night variations in CoP to
be evened out - when CoP is worst overnight it is offset by E7
electricity being considerably cheaper.

Key to Air/Ground to Water heat pumps is to really use underfloor
heating (UFH), which can directly use very low
water temperatures (35-40oC) so permitting the heat pump to operate
with extremely high CoP (5 or greater).

Long term heat pump adoption is likely to increase, but if CO2 systems
become available (CoP 5 at 0oC) then the
adoption rate globally would increase significantly. Issues then
become generation capacity and distribution, areas
where the UK electrical system may reflect the planning of its
transport system.

With most heating systems it is NOT the cost per unit, it is the
lifetime cost in terms of maintenance & eventual
capital replacement through depreciation. The latter can add 35-50% of
the effective price per unit for gas (although
realise not all heating systems are equal in terms of achieved
comfort, GCH sets the bar very high to beat).