The Hawker P.1121 and Phantom overlap

Could Britain operate both the Hawker P.1121 and the F-4 Phantom?

Probably not in large numbers; a Mach 3 P.1121 could specialize as an interceptor, but the programs overlap enough that one would likely displace the other.

The proposed Hawker P.1121 and the F-4 Phantom overlap too heavily for Britain to need both in ordinary service. If the Mach 3 P.1121 version succeeds, it could take the interceptor role while the Phantom remains a general-purpose fighter. More likely, procurement selects one aircraft and displaces the other. A specialized role split is possible, although competition between the similar programs is more likely.