Does this need capped off?

[Wingedharpy]

Me again.
New washer due to be fitted.
Cold supply only will be used with new machine.
Once the hot supply is tuned off to feed down the grey pipe and grey pipe disconnected, do we need to put any sort of cap on the end of that T piece or will it be fine just closed off?
If we need some sort of cap, would you link pics please?
Thank you.

You can screw a capnut onto the threads of the redundant valve

This one 3/4" BSP. A elderly plumber might put jointing compound on the threads, I would use PTFE tape.

Don't follow American YouTube vids as their plumbing is different.

It probably won't leak but it might be safer to get a plumber in and remove the old valve if you are sure you will never need it again, and cap off the pipe stub or use a straight compression connector.

Perfect @PigletJohn.
Many thanks.