I agree with Andy. Dealers often have rental schemes where, if it's not for you, then you just hand it back. If you want to continue, you've already paid some towards buying it.
Start out on alto or tenor. Altos are a little cheaper usually. Don't start on soprano. You may get on well, but generally, sopranos are harder to control, especially for beginners.
Do have lessons. A teacher will get you flying long before you get there on your own. A teacher often has pupils wanting to upgrade, so a good way to pick up a tried and trusted used one.
For new, these have their own brand. Well respected Company...
http://www.johnpacker.co.uk/Catalogue/JP-Instruments/Saxophones#.U713-JRdXTo
This is the biggest Sax store in the world, no less...................
http://www.sax.co.uk/
For London...
http://www.howarth.uk.com/saxophones.html
I haven't quotes any particular makes. There are so many. If you do go to a large dealer, they will not try to sell you more than you either need or can afford. It's a very personal decision. Do take advice and try as many as you can.
Also.......... they do say that the Sax is the easiest instrument to play ........................ badly ;o)))
I wish you well, Bobby.