For the OP simply go to www.insuremytrip.com and find a policy that covers the areas you want.

The UK system has been changing over the years. 100% free medical for anything and everything, for everyone, and for an unlimited time is gone. True emergencies will still be covered in the A&E but after that there will be costs. The costs will be less than in the US, and may or may not find their way to you in a bill, but they are still there.

Get a policy and feel fully comfortable that you are covered.

Many US health care policies do not cover outside the US. Most of them want what is known as a CPT code which is a medical code used in the US for insurance reimbursement. If the policy does cover outside the US make sure and understand what it does and does not cover and how to get care. Some may be very restrictive and hard to use. A supplemental policy is often easier to use.