Repair mains water pipe under concrete path

Really an onsite assesment needs carrying out to find the location of the leak if quite significant this can be detected with a simple listening device . But if it's as you say between a small area of concrete around 1.5 m then shouldn't be an issue cutting out section breaking up and then repair leak ,then shuttering and pouring new base with expansion joints ,approx 1 days work and then return visit to strike timbers

There is a repair scheme available provided by the Water Company that you may wish to consider. A similar scheme maybe provided by your supplier. https://www.unitedutilities.com/globalassets/documents/pdf/private-leak-repair-scheme-5-18-web-acc.pdf

The answer does cover somevthings but not all. Is the pipe damaged lead, if so the pipe needs renewing from start to finish, not just at the leak. As advised in the first answer an on site inspection needs to take place.

L.B Property and Aylesbury interiors have covered the problem quite well,is just worth checking you aren't covered under your house insurance (worth a phone call) and some bank accounts have extra covers on them so worth just checking

I would cut out all the pipe work in the concert and replace with sleeved pipe