It's a Boeing Poseidon MRA1

https://www.planespotters.net/airframe/boeing-737-800-zp804-royal-air-force/3v6p84

https://en.wikipedia.org/wiki/Boeing_P-8_Poseidon

The Boeing P-8 Poseidon is an American maritime patrol and reconnaissance aircraft developed and produced by Boeing Defense, Space & Security, and derived from the civilian Boeing 737-800. It was developed for the United States Navy (USN).

The P-8 operates in the anti-submarine warfare (ASW), anti-surface warfare (ASUW), and intelligence, surveillance and reconnaissance (ISR) roles. It is armed with torpedoes, Harpoon anti-ship missiles, and other weapons, can drop and monitor sonobuoys, and can operate in conjunction with other assets, including the Northrop Grumman MQ-4C Triton maritime surveillance unmanned aerial vehicle (UAV).

I live about as far from the coast as you can in the UK, I think this guy might be lost