Ancient leaking stopcock.

[Oversize]

@PigletJohn or anyone who can help please. The tap is so old it doesn't seem to have a packing nut to tighten.
Do you know a DIY fix please or will I need an emergency plumber?

Got a plumber coming via house insurance

have you got an outdoor stopcock or water meter?

It may be quite difficult to get enough movement on the pipes to remove, but in some cases you can still get a near-enough-identical stopcock to unscrew all the working parts from the old shell, and screw in the internals from a new one. A wrinkly old local plumber is more likely to have an old spare in his shed.

I think I can see the bulbous shape of a wiped lead joint underneath it.

If you have lead pipes, contact your water co and ask them to test the drinking water for lead content. There might be a subsidy or free reconnection if you replace it (this is a longer-term job than your current leak).

If not, it can be dismantled and repaired. Depending how worn it is this may last a while.

Thanks for taking the time to reply PigletJohn. Much appreciated. The plumber said he'd fixed it and nothing else needed doing. He was the opposite of a wrinkly plumber but very nice nevertheless
I'll definitely get a lead test though. The pipes in the house are plastic but it's lead under the front garden and I expect it need replacing. I flush the pipe every morning by running the tap and all drinking or cooking water goes through a filter jug. Not ideal though. Thanks again for replying.