Mr John X wrote:

How do I mitre a 7" skirting board when the deepest box available is only
around 6 " and B&Q's deep cut mitre saw only does the same ? For a couple of
cuts it hardly seems worthwhile hiring a specialist saw.

Use a normal mitre box to cut some scrap narrower pieces at the desired angle.
Clamp these on the back to cover the full height of the board and use these to
guide the saw. Only mitre external corners, internal ones should be scribed.
Bear in mind that external room corners are rarely 90 degrees and so you might
have to 'adjust' the mitre angles anyway. Small gaps caused by corners less than
90 degrees can be closed up by careful burring of the cut edges. Use a metal
roller (round part of a large screwdriver)and roll this gently up and down the
edge till the wood fibres fill the gap.

hth

Bob