I don't know an average. I get my insurance from Blue Cross/Blue Shield, it is $299 per month for me only, that with a $1000 deductible (I think you use a different term in the UK). Mrs. KF gets hers through her job, her share is $35 per month, complicated deductible but she only has to pay $35 per visit to the doctor, before the deductible is reached. A family plan is based on the age of the oldest person on the plan, for us that would be around $800 per month. My brother has two kids, his family plan is $750 with I believe a $2000 deductible. Once you turn 65 you go on the government Medicare plan, and usually get co-insurance if you can afford it, last I heard my dad complaining about it it was running around $250 per month.
Big factors affecting price of health coverage, age, deductible, lifetime limit. Quite a few self employed people are now going to $10000 deductibles. I have heard of lifetime limits of $250000, mine is $5 million.
During the 8 years I served on our local school board, one of our biggest headaches was negotiating our health insurance for the teachers and other employees. The district provided a single plan, the family plan got to be so expensive the younger employees opted out for their own. This left the older and less healthy employees on our plan, making our premiums so much higher, costing the district more. When I got off the board 8 years ago, the monthly family premium was about $900 per month.
I will make a statement about our system. If you have a good job or can afford the better insurance plans, it is great, couldn't be better. If you are self-employed, or in a job that doesn't provide insurance, it can be a nightmare if you have health problems. We needed reform, thanks to the arrogance of the Democrats who believed Obamas election was a mandate from God, and they could ram it down the throats of everyone who had doubts about their plan, we are not going to get much of anything now. I think nearly 80% of the public is convinced our system needs to be reformed, but the way the Dems went about it was never going to fly. Now that they lost the Massachusetts Senate seat, it is unlikely anything will happen.