Gardyloo has the definitive answer on airplane taxes and fees.

I'm flying through the UK on Biz class this summer. My total tax is $470 or so. I'm flying AA. If I were on BA, the tax would be approximately $950+.

The President has exempted U.S. carriers from the UK tax, so take heed on who you book for airfare.

BTW: You're getting pretty late in the game for cheap prices to Europe.

If you're including Ireland in your search, you'll probably find fares to Dublin will have the lowest initial cost. However, if your ultimate destination is Britain, then you'd need to add the cost of travel from Ireland to Britain (fly, ferry) to get an "apples to apples" comparison. The same goes with destinations on the continent - you may see slightly lower prices for the transatlantic ticket, but by the time you've added in the rail or air connections back to the UK, the total is more than it would have been just flying there in the first place. It really depends on what you want.

Otherwise, just go to http://matrix.itasoftware.com/ and put in Boston as your departure, and - like this - LON,MAN,GLA,EDI - with commas between, as the destination, using the 30-day calendar function. Once you see a fare you can live with, go to the website of the airline with that fare and you can usually reproduce it booking online.

I booked our May 2013 trip from Houston to Prague, returning from Budapest on AA back in July for $1215 pp. I thought that was kind of high but I checked the fare a couple of weeks ago and it was over $1500 pp. Glad I booked when I did because I never saw it lower than $1215.

The President has exempted U.S. carriers from the UK tax

What on earth are you talking about. All flights FROM the UK attract APDzand not even the POTUS can change that.

In fact ignore "taxes" (most of which aren't BTW) and just look at the FINAL PRICE. It's no good saving $200 on "taxes" if you spend $400 more for the ticket