There isn't a technical Deputy PM role in the UK. There was one during the coalition, to give Nick Clegg a senior role, but at the time it was commented on as being fairly unusual.
The PM is primus inter pares, meaning 'first among equals', meaning that by tradition the PM isn't more important than the rest of the Cabinet, though Blair was considered to have moved the PM role towards a more Presidential type role. There are traditionally more senior posts such as Chancellor, Home Sec and Foreign Sec, whilst DWP, Culture etc are less prestigious.
Behind the Government is the always present body of Civil Servants, providing impartial policy advice (by which I mean analysing the evidence and providing the PM or relevant Secretary of State, options with pros and cons of each). All those Civil Servants are still there providing advice, running things, and implementing the decisions made. Instead of, say, the PM, Chancellor, and the SoS for Health deciding which of the options presented to choose, it will be Raab, the Chancellor, and the SoS for Health. Raab and BJ are usually on a similar page, so it's unlikely there would be any serious change in direction.