hi, the previous answers are both good answers, but both missed an important feature. Mens and womens walking boots are made differently. They are both made to the same exacting standards but womens boots are lighter in weight, slimmer in fitting, and are generally slightly lower around the ankle.
Walking boots come in different grades, the grading refers to the seasons in which you wear them.
A one season boot will be soft and flexible and should only be worn for low level walks in summer.
A two season boot will be slightly stiffer, have a better sole, be either leather or fabric and can be used for low to moderate hills in late spring into summer up till mid September. As your from London you could wear these on the south downs, Brecon beacons, Derbyshire . Yorkshire or even some Lake district hills.
A 3 season boot is the most widely used boot for general hill walking for all the areas above plus Scotland, the Pyrenees or general hillwalking in Europe. 3 season boots are slightly more stiff than 2 season, will have a solid sole normally made from Vibram which is a v good sole for general walking. Again these are made in fabric and leather.
The final boot is a 4 season boot which isn't flexible becuse they are made to be worn with crampons. If your not already a competant walker I wouldn't recommend these for you.
All the boots made from fabric tend to have a gore tex lining so you don't get your feet wet. Some leather boots also have gore tex but it isn't necessary with a good quality leather.
The price you will pay will depend on the fabric, the season(s) the boot can be worn and the manufacturer. Go to a walking shop and try several pairs on, wear thicker socks and try and buy a pair about 1/2 a size larger than you normally wear. Your feet expand when warm and you don;t want your toes rubbing when they hot. Hope this helps.