From reading these and other articles, it seems that coverage purchased in the UK can be quite expensive for holiday travel and furthermore travelers must list pre-existing conditions. If pre-existing conditions are not listed, then they are denied coverage for these conditions should they suffer from these whilst away from home.
Luckily, UK and international travelers whatever their destination are perfectly eligible to purchase international medical insurance plans from US companies. Policy costs are usually very economic compared to European policies, especially if travel does not include the United States. Travelers can use our Visitors medical insurance comparison tool to compare prices and coverage of different policies. Some policies offer coverage for pre-existing conditions (there is no list of diseases to be mentioned in the application). Be sure you select your destination as either "US only" or "all nations including US" or "all nations excluding US" and your citizenship as "US" or "non-US" to get an accurate price quote.
While comprehensive travel health insurance plans like Patriot America Plus provide coverage for acute onset of pre existing condition up to the age of 70, comprehensive plans like Atlas Travel and Atlas Premium from Tokiomarine HCC extend their coverage for acute onset of pre existing condition for the age range of 70 - 79 with a policy maximum as high as $100,000 to $250,000.
Atlas Travel plan:
Atlas Premium Insurance:
Safe Travels USA Comprehensive can provide coverage for acute onset of pre existing condition with a policy maximum of $50,000 for people above 65 up to age 89.
Safe Travels USA Comprehensive:
Liaison Travel plans is another set of very good comprehensive plans with worldwide coverage availability for people traveling out of their home country.
Liaison Travel Elite
Liaison Travel Basic
Liaison Travel Choice
A holiday experience should be relaxing and as carefree as possible. Insure yourself and your loved ones before you travel for peace of mind and for help with your medical bills should you incur any! As always, we wish you safe and happy travels.
INF travel insurance

List of plans :
Premier Plan Choice Plan Elite Network Advantage Plan
Compare INF plans
Fixed Benefits Plans Comprehensive Plans