There was a great deal of experimentation with the .50 BAT round undertaken by Kynoch in the UK, but the only British round that was approved for service was the L10A1 drill round. For operational use the US made M48A1 was adopted.
Although there were inert filled British experimental rounds made, none of these saw service and I know of no use of American practice rounds in the UK.
British experimental rounds utilised both US type open nose projectiles with a primer/detonator inset or normal spitzer type with incendiary composition in the nose. There was also a case type with a screw in promer with flash tube.
Here are some British examples.