In the event of a leak, first turn off the water at the main valve; if you smell gas or see sparks, switch off the power at the fuse box. These two actions often prevent further damage before a specialist arrives.
When you submit a request, please describe the problem as accurately as possible — what the problem is, how long it has been going on, and where it is happening. That way, the engineer will arrive with the right tools and resolve the issue on their first visit.