OK, so I found out that my drill won't fit between the joists (between
ground floor and first floor) with a 25mm bit in it so I'm looking for
a right angle drill or a right angle adapter.

I found this one:
http://www.screwfix.com/app/sfd/cat/...08869&id=19979

Not cheap and probably wouldn't manage 25mm through a joist.

This is cheap but doesn't look like it would cope either:
http://www.inest.co.uk/range.asp?typeId=603&id=539

Any other ideas?

(I realise I can very easily cut a notch in the top of the joist but
a drill is quicker, neater and easier - it will also mean I can put
the pipes lower down in the joist which will stop them from heating
the very creaky floorboards causing expansion and banging.)

TIA

Mr F