Jacob Thomas wrote:
I am fitting a new bathroom basin. The centre of the existing trap
reaches approx 15cm from the wall but the plug hole for the new basin
is approx 20cm from the wall and 5cm higher. The waste pipe is
cemented into an outside wall so not easy move or replace. I think a
telescopic trap might solve the 5cm height difference but what can I
do about the other gap - are there traps available where the ubend bit
is telescopic as well?

There are all sorts of traps available - look at BES.ltd.uk for a good
range. Screwfix & Toolstation have a narrower range, your sheds and PMs
will have some ...

Sounds as if a telescopic trap plus short extension to the existing pipe
should do.

Alternatively what about connecting to the bath waste pipe which runs
along the skirting behind the basin is this allowed?

Should be OK as long as the run from where you'd join the pipe to its
outfall isn't too long and/or shallow, or you might get water backing up
into the bath when you empty the basin.