How can I safely have 2x 7kw/32amp electrical vehicle chargers connected to my consumer unit? (UK)
The most important thing to check is probably the size of the main supply fuse on your incoming feed. Between 60 and 100 amps is typical for a domestic supply. If you have a 60 amp fuse, I'd be very wary of trying to run two chargers at 7KW each simultaneously.

The other thing to consider is the actual consumption of the chargers that will be connected. Just because the supply point is rated to 7KW, doesn't mean that the charger will actually draw that.

You don't need to accommodate the full current capacity of all the breakers because you're unlikely to be using everything that you possibly can at any one time, but if your peak load exceed the main fuse, you have a problem.

Personally, I'd be very tempted to have nothing further to do with British Gas and approach a local electrician about the work. If their electrical work is priced like their plumbing, it'll be very expensive. (And I wouldn't be surprised if they subcontract it out anyway).