What's the best lock I can buy in Manchester tomorrow?

Tools to kill a D lock:

Jack

Tools to kill a cable/chain lock:

big cutters.

Chances of a robber carrying both are slim as they're both bulky tools, so use one of each type.

Not really 100% correct. Not like all D locks can be levered open, or are impossible to cut. Not like cutters are the only thing that can break a cable or chain.

Using both is a good idea though, D lock can fit will around rear wheel and seat tube and a cheap cable for the front wheen and downtube. Also if youre in a spot where you cant fit a D lock you can use the cable.