John Laird wrote:

I now have a small submersible sump pump, which will be installed in
due course ... I bought one which will deal with small particles, so as not to clog
with the silt coming off the concrete, and which claims to pump down to
8mm minimum depth, as I was hoping to use it to clear most of the water
that has gathered at the moment.

But... the pump won't get "started" in the 2" deep area of the puddle
that I can easily get to.

Is it possible that you've bought the wrong pump?

I've had a problem in the cellar for years which lets the water in when
the water table rises far enough. It is entirely unpredictable - no
sign of water despite the amount of very heavy rain we've had recently
(although it usually takes a few weeks before anything starts
happening...) Strange thing is it might not happen for 2 or 3 years
then it floods twice in a year! - and when it does it seems to come in
rather rapidly!

I bought a "Hippo" fully submersible pump (from Argos, if memory serves
me correctly) some years ago because it claimed to pump down to ~4mm
(which it does) and placed it in the lowest part of the cellar, which
is about halfway along . (Obviously we don't keep anything of value
down there and what there is is kept above "high tide" level!)

It stays in place all year round and, to avoid paddling, the mains lead
is coiled up on a hook by the cellar door. At the far end, the end of
the hose is tied onto the underside of old iron coal hole cover. When
water appears, the mains lead is plugged into a socket in the hallway,
the cover of the coal hole is removed and the end of the hose pulled
into the open and off we go!

It works perfectly: the pump never blocks (instructions are to connect
hose to water tap and flush it out backwards if necessary but its never
been needed) and the motor runs in oil and is rated for continuous
running, wet or dry, so I just leave it running and check it
occasionally until it has finished!

The important thing is that it will pump water at any depth above 4mm -
so long as the input vents are covered, it works! This was a major
consideration because there is a peak in the floor at the bottom of the
stairs which traps ~12 - 15mm of water at the end. When the main part
is pumped out, I leave the pump running and use a yard broom to drag
the water up and over the top. Every time sufficient water runs down
the other side to cover the pump inlet, off it goes again, so we are
left with very little water at the end of the day.

(One of these days, when I get a round tuit, I'll smash down into the
concrete to create a sump!)