I just went through this strange exercise myself. I called Anthony Gold but it seems they do their wills out of their Streatham office. If you travel there it's £350 for a simple will. If they come up here to the London Bridge office or your home it's another £100. I used LZW on Bermondsey Street, still £450 for basic service. Either way I'm sure you'll get competent work. Lots of lawyers do this sort of work. There's also a group of non-lawyers called the , Institute of Professional Will Writers. I don't know much about them other than they'll be somewhat cheaper than lawyers.
You need to think a bunch of stuff through. Obviously who you want to leave your home, possessions, cash, savings & any investment to. The UK lets you leave £350,000 worth of value without taxing it, everything above that gets taxed at 40% inheritance tax. There are legal strategies to reduce the taxes but I suspect getting into that topic costs £. You also have to decide who is going to do the paper work when you die. This is called your executer. It can be a spouse, friend, relative or a solicitor. You may also want someone to act as your Lasting Power of Attorney for if you're incapable of making decisions yourself at some point, eg dietary issues if you're in care, prefer care at home and other tricky issues if you can't make the decisions yourself.