Stepwilk, You may find this interesting, its an article in Flight by the Princess designer:
1952 | 0651 | Flight Archive
These pictures linked on the Secret Projects site referred to by tornadoken are well worth a look.
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I'm going to email the link to my uncle, as he worked at Saunders Roe and was a flight test observer on the Princess. He may know if there was ever any mention of a patrol bomber requirement.