On Wednesday, 25 January 2017 17:03:54 UTC, Simon T wrote:
Am currently installing a new bathroom suite.

Removed the old toilet to tile behind it. Went to fit the new one, only to
find the new tank is a lot smaller and doesn't touch the wall, leaving a
40mm gap (or thereabouts).

Can't push the toilet pan back any further. So, is it a case of taking the
pan back off and cutting the soil pipe back by 40mm, or do I just use an
extra long screw and some sort of spacer?

If it's not close coupled, you need a new longer (horizontally) flush pipe. Cut to suit.