It is an interesting question and one that I couldn't find a proper question for within the UK Government pages on interpreting the law of intestacy. There does not seem to be a clause to cover the situation of spouse deaths within a short period of time.
UK death certificates issued by the Registrar record the date, but not the time, of death.. This information is taken off the death certificate issued by a doctor which does record the time, the date and the place of death. However the 'time' information gets 'lost' in the formal document.
I suspect, therefore, that if there is an intestate situation where the same date of death applies to the married couple, the each partner's personal estate is dealt with as if the spouse did not exist from an inheritance point of view.
However if one partner survived long enough such that a later date appears on the death certificate, that (longer-surviving) partner's family take precedence for the sharing of the estate.
This surely must have been tested in the courts before now - but I couldn't find it.