Alistair, do you mean an attorney above and beyond the real estate solicitor? I'm not an expert on these matters, but we're in the process of buying a flat at the moment and we've only needed to hire one solicitor, who specializes in real estate.
I'm sure there are more issues than we've personally covered, but in our experience we've had to deal (lengthily) with issues regarding repairs to the flat (ask if they're the responsibility of the freehold/landlord or your own/the seller's), and finding out about general repairs to the building, such as whether or not there's a "sinking fund" in place for any external maintenance, and whether the sellers have been paying into it; also, when any general repairs are likely to take place - you don't want to move in and then get directly smacked with a huge bill for your share of the renovations because there was no sinking fund. (On the other hand, if the property is in need of maintenance, you want to know that you won't be left with fraying carpet and peeling wallpaper in the communal areas forever.) You also want to know how much ground rent is, who and how the property is managed, and any other recurring costs that you're responsible for throughout the year.
Your solicitors will be the ones to find out all of these things - as well as other, similar issues - for you during the buying process. Essentially, their job is to align your interests with those of the sellers', represented by their own solicitor. It can take a very long time (especially in our case, with coordinating the necessary repairs), but most of this time is taken up with the solicitors exchanging proposed contracts between each other until all parties are satisfied.
Definitely take your mortgage paperwork, if it's available. Have you already gone to a mortgage advisor? I recommend going to one straight away, because they have access to many mortgages offered by multiple banks, rather than limiting yourself to one bank and only the options they provide. In this economic climate, you want to get the best rate possible. Shopping around is to your advantage.
It doesn't matter if you get your mortgage or your solicitor first - they're two separate, but both necessary, services. Just be sure that you have both as soon as possible - the estate agents and the sellers won't be inclined to do business with buyers who don't have a firm mortgage offer and aren't taking steps to close the deal by hiring a solicitor.
Anyhow, good luck! It's exciting to be buying a new place, and the better prepared you are, the less painful the process should be. Get some recommendations on a good solicitor from friends or online review sites like yelp.co.uk or qype.co.uk. Hope it goes smoothly for you!