I agree with that, my issue is that we pay £170 more to buy stuff from the same company from the same warehouse just to have the website in English.
That has always been the case though. Companies set prices based on what they think the market will pay, nothing else.
For a quick comparison: GDP per capita is $44,118 in the UK and $37,728 in France. If all else is equal (taxes, living c0sts) then the average Brit has 17% more cash, and a £665 lens is France is vaguely similar to £780 in the UK as a measure of expendable income. But that is only a small part of the equation, perhaps British People are just as liekly to buy the lens for £170 than the French, in which case the company has set ideal pricing.
I you don't like it then you have 2 options:
1) Buy a cheaper lens, in theory companies will realize the sales differences and prices will adjust to maximize profit which would mean lower sales price in the UK. This only works if a majority of people feel the same.
2) Take full advantage of the EU single market and buy the lens from France/Germany etc. without worry over additional taxes.
Really, at the end of the day the British market is known for accepting higher prices for products. The same is true for anything from cars to TVs.
When I was a kid we would get a channel ferry to France every summer and go camping for 2-3 weeks, we would always book the ferry form a french website because the french prices were cheaper, e.g P&O with french language options was cheaper than English language version. Nothing illegal about that at all.
My Subaru Forester cost about 1/3rd of the price of the UK equivalent model (I'm in the US). The funny thing is I could get a second hand Forester a few years old cheaper in the UK than the US, because int he US cars depreciate way less because they are far cheaper new.
Even within a country there can be big price differences. There have been cases where companies would distributed special offers only to select regions of the country, or the offers would vary by region, and in fact some companies would print their sales brochure with items at different list price so if you lived in Manhatten you would get prices quoted 20% higher. than the mid-west. Same has been shown for online purchases, e.g. if you connect via a mac or Ipad then the company hikes up prices. All of this has been taken to court but thrown out because it is perfectly legal to set prices differently for different people as long as you don't discriminate on race/gender etc.
Just last year I was booking a flight but the prices jumped up $200 over the coup[le of day looking. I got annoyed and called my wife, she doubled checked form her office and got the original price we had found earlier in the week. I cleared all my cache but was stuck at the higher price so called back the wife to book. They had obviously logged IPs and had fixed the price.