FWIW it is not illegal (therefore it is 100% legal) to descend below the MSA, in a G-reg, in UK airspace, for the purposes of a landing, on a DIY "instrument approach".
You are always open to the "reckless" clause in the ANO but
AFAIK this has never been used in these cases.
For an N-reg it is illegal worldwide; FAR 91.175 refers.
In practice, people routinely descend over the sea, to get intoa coastal airport. Just be extra careful watching the altimeter
And be really extra careful watching it at night
If you have an autopilot with VS/ALT modes, use it to the full while monitoring things.