The Boulton Paul P.97 was a design for a twin engined night fighter produced after the Air Ministry decided that its F.18/40 specification couldn't be filled by a single engined fighter.
F.18/40 of August 1940 called for a two-seat night fighter armed with six 20mm cannon. Boulton Paul produced the P.96 design, a single engined fighter that could have been armed with a Defiant turret and wing guns or just wing guns, but the Air Ministry then decided that the specification required twin engined aircraft.
The P.97 was a twin boom fighter. The crew would have been located in the central nacelle. The twin engines were carried below the wings, and booms ran back from the engine nacelles to twin vertical tail surfaces. These were connected by a single horizontal tail surface.
The P.97 was designed with several alternative armament layouts. The most conventional had fixed forward firing cannon and the A Turret from the Boulton Paul Defiant carried above the wing (P.97B). There was also a version with the standard cannon but without the turret (P.97A). A raised navigator's position replaced the turret. In both cases the six cannon were to be carried in a weapons bay within the central nacelle, below the mid mounted wings.
A more radical version would have been armed with twin 20mm cannon, carried in slots on either side of the nose, and capable of moving up or down. This would have been for ground attack missions, allowing the aircraft to fly level while hitting ground targets. Although the P.97 didn’t get built, the movable cannon concept was used in a modified form on the post-war Avro Shackleton.
The P.97 was rejected for being too radical. It was similar in layout to the Northrop P-61 Black Widow, also a twin boom night fighter. Work on the P-61 began in 1940, it made its maiden flight on 26 May 1942 and didn't enter service until 1944, so in this case the Ministry would appear to have been correct.
Boulton Paul were involved in the winning project, a two-man version of the Gloster F.9/37, but this project was cancelled on 1 May 1941, by which time it was clear that the de Havilland Mosquito was going to fill the night fighter role.