In article ,
fred writes:
These are intended for this job:
http://www.screwfix.com/prods/36622/

They're meant to be fitted under the felt so that any leakage past the
tiles runs off the felt, onto the tray and then into the gutter. Fitting
is easiest before the tiles go on but a retrofit with you just lifting
the tiles shouldn't be too bad. The weight of the tiles may be enough to
hold them but a self tapper into the gutter would make it more secure.

As you appear to have had the bad bunch out, I don't imagine there's any
risk of the tile fronts being clipped down.

I've never found a house with the bottom row of tiles nailed down
(and usually, no rows are nailed down except possibly on the edge).

I've fitted these by sliding the bottom row of tiles up under the
row above. Then slide the support tray under the felt. You may need
to trim the lip on the tray so the tray rests on the rafters, and isn't
being propped up by the gutter. Hold the tray in position with a nail
or screw into each rafter near the top edge of the tray. (Lift the
felt to do this -- don't put the nail/screw through the felt.) I used
galvanized roofing felt nails as I had them handy at the time, and the
top doesn't have any sharp edges to tear the felt. Don't fix them to
the gutters, or you'll have problems with differential expansion and
you'll curse if you ever want to take the gutters down.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]