Hey,
this is all mutual fund stuff? I don't *think* you'll find much help here (I could be wrong) - just not many Brits doing mutual funds here.
I have some UK stuff (expat) but those are ETFs. If you're reading Monevator and other UK-focussed stuff (Simple Living in Suffolk is good, though he is a stock chooser rather than passive) you're probably going to get more sensible answers. I think Money Saving Expert has a ranking of all the brokers, or a list of them rather with all their fees and such.
My.. gut feeling would be two fingers to any company charging any kind of entry or exit fee. I would rather go down the ETF route where you pay to buy, pay to sell (~5 pounds to the brokerage for each, or less for a 'regular investment', with the broker I use - iWeb), and the only other fee is the MER of the ETF. But that is my choice, and I don't know anything about Alliance Trust.
Just for comparison: For, say, the FTSE 100, you can buy an HSBC ETF with ~0.35% MER. The Vanguard ETF (VUKE) is a smidge cheaper but you will get US withholding tax *I think* - because it's not Irish or Luxembourg domiciled (I think it's a LSE-listed wrapper for the US-fund containing the LSE-listed stocks which is.. silly.. but probably cheaper for Vanguard to do).
Anyway, as they say: DYOR :) Good luck!