In uk.d-i-y, Dave Liquorice wrote:

H&S rules means that BT engineers should not go into lofts. They are
rather hazardous places, not to mention feet through ceilings etc...

However if access is via a proper loft ladder through a decent sized
hatch (2 to 3' min) into a roof space that is well lit and the floor
is securely boarded over for all of the access a BT chap needs and the
socket not tucked right down in the eaves then you can probably bribe
any engineer that visits with cups of tea and chocolate biscuits...

Exactly my experience when getting an ISDN line put in at my previous
house: it made most sense to run through the loft close to where the
existing cable from the pole attached to the property, running from front
to back of house over to just above the corner of the bedroom where I
wanted the socket. So the day before the BT bod came, I went up a ladder
and put in a draw wire through a little hole in the soffit/eaves/whatever-
you-call-that-bit, and another from bedroom to loft. The loft had boarded
walkways and light. When the BT engineer came, I stared with the obligatory
tea & biscuits, then showed him the prepared route, and he was a very happy
bunny to have had the route worked out, draw wires prepared, and loft
timbers to drive cable clips into at speed rather than ever-so-careful
surface-running around doorframes and the like in the way they so often end
up doing. He put in the transition box from external-black to internal-white
at a handy point in the loft, and put the ISDN termination box at the
requested spot in the bedroom, with the BT cable coming down a handy-dandy
bit of trunking I'd provided. Job done to both parties' satisfaction...

Cheers, Stefek