The original post on this is misleading and ill-informed. In the UK there is no restriction over congested areas - all helicopters must fly in accordance with rule 5 at 1000ft above the nearest highest object within 600m. Single, twin or triple.
Police have exceptions to that - and it is they who mandate twins. This policy deprives many areas of the UK from the taxpayer-funded benefit of police helicopters.
There is a restriction on CAT landing sites for singles - purely take-off distance related. This needs addressing because it appears to apply random outdated data to some singles.
And there is a restriction on SEH (and SEP) CAT at night.
Other than the ridiculous outdated "floats on singles" for ops through London, that's about it.
Yes - twins can get better Rule 5 exemptions. But the vast majority of CAT and private work onshore can be done by singles.
Doesn't please the twin operators. And doesn't fit into the brain of an ex-mil CAA regulator who's been taught that twins are safer.
Any SEH restrictive regulations are way overdue for examination - they are based on data that is some 40 years old.