It is hard to believe for Americans but there really is no need for cover at all in the UK. Several posters have said that. Some time ago I had an appendicitis attack whilst in the UK as a visitor. The entire cost to me of a three day stay in Hammersmith hospital, the operation and post-operative care was Zero.

Don't worry about it. Just be happy that the UK spends around 2/3 what the US does on medical care and all comers have free emergency and accident treatment, even tourists.

if you really want to have a wonderful hotel, I mean hospital, try this one:
http://www.thewellingtonhospital.com/info.asp It has separate rooms for your companions to stay, a wonderful menu for room service, luxurious accommodations, and for Americans an additional benefit: you must pay for it. Because it is provate it has hefty fees. Sadly, it is still much cheaper than the US ones, but it has the advantage of being an excellent hotel. I stayed there for a week when I had a relapse of the infamous appendicitis problem. My US insurance paid the bill, but I had a nice copay, still less than my hotel charges were before I went there.

The US is an excellent place for a foreigner to become seriously ill.