The Hawker P.1134 was a project for a research a/c to ER.180D for speeds
up to Mach 4. Several different configurations were planned and the P.1154
somehow resembles the Delta. And the designation P.1154 was given to the
joined RAF/RN supersonic VSTOL fighter.
You might want to find more info (e.g. specs) on the P.1134 in the volume British Secret Projects: Hypersonics, Ramjets, and Missiles, since it contains info about hypersonic machines, and the P.1134 was Mach 4 capable.