MDPE 32 or 25mm into the house

[Riley]

I think the answer without seeing is that 25mm should do what you require however they could've carried on in 32mm

 

[joni os]

So does this mean the builder was correct to downsize to 25mm, or could he have carried on with 32mm inside the house to the internal stopcock?

He should have asked the question and you should have asked a plumber. Hopefully the internal stopcock is to 22mm copper as is your cold water feed to unvented. A G3 plumber should sort out cold water balance to shower and bathroom fittings together with necessary non return valves. The benefit of replacing 25mm with 32mm can then be assessed.