I wonder whether those wanting to "crack on with it" are aware how pitifully unprepared the Government is for implementing a Leave vote - not just (just!) as to any policy plan, but also as to the sheer practicalities and resources required in the period immediately following an Art 50 negotiation.
If a new trade deal is to be negotiated with the 27, and then separate deals country by country with the rest of the world, you need a lot of experienced, highly competent and probably multilingual trade negotiators. (The 27 have said/hinted that they will seek to negotiate in French, rather than English).
You also need a lot more lawyers than the Government currently has, not just to deal with trade arrangements but also to review the whole body of law enacted since accession to the EEC - thousands upon thousands of statutes and statutory instruments - to identify and implement the complex further legislative steps which will be needed.
We don't have lots of home-grown international trade negotiators (tens rather than hundreds). We haven't needed them much since the 1970s, because trade deals with the rest of the world have been negotiated by the European Commission on a collective basis. Most of our good ones actually work for the European Commission, so they may not want to, or be in a position to, switch sides. It's a recruitment headache, no doubt.
By all accounts the massive headhunting exercise for lawyers which was launched by the Government Legal Service after the referendum result isn't going that well either.
"Crack on" sounds simple, but when time starts ticking towards that very tight 2-year deadline it is all going to be very far from simple.