It is against the rules, but as long as you used a different address two accounts wouldn't be spotted. However, your BA Miles would be spread across 2 different accounts which would make redemptions harder.

Personally, giving up the Amex '2 for 1' (and the ability to convert Tesco points) is NOT worth the benefits of accelerated Silver. This is the main reason keeping most people on this board from moving their accounts to Europe.

If you want the lounge access and business class check-in benefits of Silver, do an American Airlines Platinum Challenge (which will get you AA Plat = BA Silver from one long-haul, even in economy). For lounge access, you could join Qantas Club (£250 year 1, £100 thereafter) which gives the holder and a guest BA lounge access when flying BA, and similarly on other OW airlines.

Anyway, you are only 100 tier points short of Silver. You can get these from 2 Club Europe weekend flights in the next 8 weeks, sub £200 each if you pick the right places (Naples, Marseille, Prague, Dublin, Paris).