On Saturday, 4 July 2020 12:59:48 UTC+1, polygonum_on_google wrote:
Trouble is, cost of P&P makes online prices quite high. I can get
suitable tube locally at a reasonable price and avoid P&P but,
so far, have not found anyone to supply threaded both ends tube.

If 20mm or 25mm steel electrical conduit is stiff enough, Conlock?

http://www.discount-electrical.co.uk...conduit-boxes/

Heavier than that is Kee Klamp.

https://keesystems.com/store/fittings.html

Or find someone who does gas meter fitting and is used to working with gas barrel.

You can also hire electric pipe and conduit threaders

https://www.hss.com/hire/p/electric-die-stock

Owain