All league tables are estimates. I went to Surrey and would 100% say it deserves to be highly ranked, but as others have pointed out, its position relative to other big players seems a little suspicious.
I would simple say that it is hard to compare universities when each university has its own individual strengths. Apples and oranges as the saying goes. Also the league tables don't factor in prestige, but prestige may lower rankings due to students expecting or demanding more from the course they are on or from the university in general.
In my opinion the league tables are nothing more than a very rough guide and you should assess individual universities yourself. Just because a uni is highly ranked doesn't mean it will suit you. A few places or tens of places in the rankings doesn't mean much in the real world.