Removing existing tiling is a lot of work, so it depends how much you have already.
And the walls may need to be replastered. That could easily be £800 and can take several days to dry.
Depends how much they have allowed as cost of new tiles - they may have priced it on £50/m tiles , so that will be a fair bit to do the whole room.
Tiling a floor can be a lot in labour costs, depends on your sub floor.
Are you moving the position of any of the fittings ? That’s more work for the plumber, especially if you move the WC.
Are you getting extra lighting, wall lights, electric or dual fuel radiator, heated mirror or shaving point that needs power? All work for an electrian.
For labour you could easily be
800 for plasterer
1000 for tiler
600 for plumber
200 for joiner
100 for electrian
400 for labourers to rip it all out
John Lewis will have allowed a lot of ££ for fittings.
Does the quote also include wall cabinets, a mirror, supply and fit of heated towel rail?
Don’t forget skip hire and you are paying for someone to coordinate and supervise all this work.
My guess on your quote is at least £7k.