Halstead, a tech entrepreneur, was the Ginetta GT5 Am champion in 2018 and has had a pole position in TCR UK this season.
His Clio Cup weekend will be sponsored by Infosum and ThroughtRiver and he will race the car campaigned by Westbourne's joint Team Principal James Colburn at Croft in June (pictured left).
Halstead, aged 47 from Hampshire, said: “This is a great way for me to race in front of the BTCC crowds and get my name out there a bit more.
“Hopefully I can mix things up a bit at the front and this will also give me more practice in a front-wheel-drive car.
“I’ve watched the Clio Cup for a few years and I love this type of sprint racing which is almost made for the short Silverstone National circuit configuration.”
Halstead’s outing will boost Westbourne’s line-up at Silverstone to four cars.
It has fielded cars for Ben Colburn and Finlay Robinson all season and yesterday Anton Spires confirmed a return to the squad for his home event at Silverstone as well as Brands Hatch's season finale.