First of all who is the house builder?
Clearly you were sold one thing and are expected to buy something less.
This is not allowed in law and is also against the requirements of the Consumer Code for House Builders too! If they wont give you £1,000 for the missing wardrobes, make a claim using the
Code Adjudication Scheme.Don't forget to add £250 for "inconvenience" and ask for the £120 fee to be reimbursed too.
You will need proof of the wardrobe such as a brochure or a written specification.
I would question why your particular flat has a "lack of space" Could it be that a wall is in the wrong place making the bedroom too small for a bed with the wardrobes?
My advice would be to insist that either they put the wardrobes in or if this really is not possible, you buy another flat which does have space for wardrobes for no extra cost to you.
I hope you have not used the house builder's choice or suggested solicitor.
But it rather sounds like you have and you may now realise why this is a very bad idea!