Did HSTs from other operators run on the mainline west out of paddington in 2015/6?

Hi All,
Trying to decide whether there is a base of fact to allow me to keep my fleet of HSTs from operators other than First Great Western/GWR to run on my WR Main line layout in its 2015/6 version?

I know in the early 2000s Midland Mainline and GNER sets or power cars were used in times of poor fleet availability or peak demand, so I wondered if this practice still happened in 2015 or 2016?

Details of observations/links to other relevant posts or magazine articles would be appreciated.

Many thanks
Paul