Thanks both.
The feeder from the street is under a manhole cover straight out front, so I should be able to get to that easily enough. Would definitely go with a new valve, rather than a fettle on the old one. Will have a look this week for Conex locally.
Re the SureStop, that sounds good. Was concerned how the two could play together but assuming there is a design specifically for installations with a stopcock, think I'll go for this at the same time as the new valve.
Thanks again
BTW, sorry for the delay replying. Although I've checked the option to be notified of replies I don't seem to be actually receiving notifications.