I got a water meter fitted and my plumbing started making a noise. A new ball valve on the main tank cured it. I think a new washer would have been enough as it was a bit scaly. Is that within your plumbing capabilities for a cheap and easy fix?
Not worth the hassle of mucking around with washers when a new ball valve is so cheap and so easy to replace.
It's really a DIY job if the OP has a spanner and knows where his stopcock is (and verifies that it works)