Hmm, interesting. I have Nationwide buildings & contents and they are now underwritten by UK Insurance who are basically Direct Line.
Kind of tied to Nationwide or at least anyone who will cover a place considered at risk from flooding, even though it’s never been flooded but it’s got close.
As for under insurance, the policy needs to specify an averaging clause, plus it looks to me that it’s not a problem if it’s a full loss.
http://www.financial-ombudsman.org.uk/publications/technical_notes/under-insurance-household.html
e.g. their formula is “(sum insured / true value) * loss = payout”
so (£1500 / £3500) * full loss of £3500 = £1500. So you get what you insured it for.
But if someone nicked just the forks at say £500 value…
(£1500 / £3500) * loss of £500 = £214 payout.
Anyway, the amount you are insuring for depends on whether they are asking for the full retail value or the current market value.