Just looked on a British govt site for you. They state that although credit cards should work as usual, smaller shops and restaurants could be reluctant to accept them, preferring cash, as shopkeepers may have trouble gaining money from their own accounts, which are restricted.
However there have been reports in the British press recently of tourists not noticing any difference at all. Whether this reflects on the type of tourist or their spending habits is open to speculation. Being on a flotilla and potentially not able to get to major towns and/or banks, I think I, personally, would take plenty of Euros in cash. From our Press there are very mixed reports as to what is available or not, and costs of living. Again, could be down to the tourists questioned. Overall I think I would not rely solely on credit cards.