The car will not pass an MOT if the ABS light is on.
you have more rights if you bought from a trader with no warranty (as some warranties are little more than clever wording not to pay out for much)
You need to tell the dealer that you understand your rights as a consumer (you need to know them yourself first too) and explain that he does need to take some responsibilty...
It is a few years old - 3-4? but has done low mileage, so a reasonable settlement would be that he pays a large percentage of the bll to fix, say 75%, the typical labour payout is 30 odd quid per hour, if the garage charges more than this you pay the rest yourself.
You may not be able to claim back diagnosis, and if it turns out to be an abs sensor, which is a wear and tear item, then don't expect too much at all.
But thats typically what should happen with a fair trader.
And a fair trader may ask you to select another car from his forcourt and settle on any monetry differences should the 147 repair bill seem excessive.
Trading standards will take a fair view, for every bad trader theres probably 10 bad consumers trying to screw money, they will take a stand of whats fair wear and tear considering its age, mileage and market value - which is why you can only really expect a percentage of the repair bill to be paid.
Start by asking if the car was sold with any warranty or if you are covered on the sandard sale of goods act -