In addition to your budget, you need to consider the terrain, your height & fitness, and your ego ...
If the bike is for pavement & tow paths, then your bike really doesn't need ANY suspension ...
And, your focus should be on wheel AND tyre size ...
By my arbitrary reckoning, if you are 5'9" or taller, then you may want to give serious consideration to a 29er regardless of the suspension-or-lack-of ...
If you are shorter than 5'3", then you will probably want to stick with a 26er ...
IMO, the 27.5" wheels-and-tyres will depend on terrain and/or your rider skill & fitness level -- as I told the manager of one bike shop when I realized I had mistakenly picked up a tube for a 29x2.3 tyre & was exchanging it for a 29x2.1 tube, "I'm not man enough to handle a 29x2.3 tyre."
With your budget of £700, you should not have a problem finding a suitable bike ...
Use GIANT's line of bikes as a benchmark for value for your Pound ...
After that see what the other brands of bikes may-or-may-not have that whatever Giant bike you choose to use as a benchmark does-or-doesn't have.
THIS is where your ego comes into play, BTW, because some people want a fancy-schmancy name on the downtube.