I think it was the Miles M.52, there is an original scale model at lovely little aviation museum[1] near Reading, England.
There is also a very good reason the Bell X1 looks very much like the Miles. [2]
> In 1944, design work was considered 90 per cent complete and Miles was told to proceed with the construction of a total of three prototype M.52s. > > Later that year, the Air Ministry signed an agreement with the United States to exchange high-speed research and data. Miles Chief Aerodynamicist Dennis Bancroft stated that the Bell Aircraft company was given access to the drawings and research on the M.52;[16] however, the U.S. reneged on the agreement and no data was forthcoming in return.
[1] https://museumofberkshireaviation.co.uk/html/exhibits/m52.ht...