depends really the DSA say it is bad practise,but all the advanced groups ROSPA and IAM say it is bad practise unless manouvering
I do recognise the merit in those concerns as there are a fair few drivers about who started their motoring experiences by driving manual gear change vehicles with the (usual) requirement to brake using the right foot to stop it when necessary.
I suppose the concern is - now that many of such drivers have migrated to vehicles having automatic transmissions with some adopting the (entirely natural) two footed approach - there may well be the tendency for them to hesitate in applying the brake or applying both the brake and accelerator pedals in the event of an emergency when old practices have a habit of coming to the fore – no time to think; instinctive reaction, that sort of thing.
Police driving (at advanced/other duty standard) bears no resemblance to the civilian counterpart(s) and different operating practices are necessary to accomplish the task at hand. In that regard I always found that the two-footed technique allowed me to attain and maintain the speeds necessary to get through traffic as safely and as cleanly as possible.
To drive an unmarked vehicle at speed through a city/urban environment is difficult at best (and downright dangerous at worst) but the two-footed technique allowed me to deal with many such situations without too much drama.