First of all, don't plaster this forum with multiple posts on the SAME ISSUE!
It wastes my valuable time.
I've answered your post below. Thanks for mentioning elsewhere, it was a completed home built by Taylor Wimpey.
I hope you don't exchange contracts until this is addressed.
Extensive works will be required in the neighbours property comprising of excavation to below your garage floor level, then a waterproof tanking applied to the garage wall from foundations to at least 150mm above ground level (neighbour's side). Then the tanking will need protecting, usually a 100mm skin of blockwork, and the top of the tanking and protection should be have a lead flashing cut into the brickwork 25mm, pointed and dressed over the wall.
If the builder refuses to address this you will have all the information you need to walk away.
If you exchange contracts, you will be forced to legally complete and have a long drawn out battle with the builder and perhaps the NHBC trying to get the work I outline above done.