hey mate nightmare!
this happened to us about 2 years ago in November... almost exactly the same situation as you!
We were faced with the 'one free attempt to locate and fix' or '£200 if you fix it yourself' choice from the water board.
the leak was right under my driveway! it flooded the whole front garden like a swimingpool.
We had to have the water off for a couple of weeks or so.
I figured it was a galvanised iron pipe probably from when the house was made, so the 1st free fix option was never going to help.
ended up fixing it all myself with much help from relatives. It was a job and a half, we had to dig up a channel all the way up the drive to get to the pipe which was a long way down, had to get through a good thick amount of concrete, was hard work!
nearly chopped a gas pipe in the process (be careful if you do it)
had to pull the whole run of iron pipe right out, it was a length that ran from the road right down the drive and right under the house front to back! it terminated at the back of the house at the copper house plumbing.
Anyway the old pipe was shot to bits in many places so a complete replacement was the right thing to do in the end. We could have done a short term fix on it but it wouldn't have lasted long tbh.
It was a bit of a job but we managed to run the new blue plastic pipe right from the road to the back of the house, feeding it right under the house from front to back, exactly where the old pipe went!!!
It's been fine since, a job and a half though and to get builders/plumbers to do it would cost a small fortune, and then some!
if you need any advice can probably help...
the cost of the parts was like £50 or less so we made £150 profit in the long run, the effort was considerable and it was a right pain in the arse.
Bad timing for you mate, I really really feel for you right now