Detecting is allowed on most council-owned land with no permit, provided the national Code of Practice is followed; the council says beaches are fine. The page does not say which stretches of beach the council actually owns, and Morecambe Bay is an SSSI.
"Beaches and shrub land are fine. ... A permit is not required for metal detecting, but there is a requirement to adhere to the code of conduct mentioned above."
Tap any spot in England on the UK Detector map to check it against scheduled monuments, SSSIs, nature reserves, National Trust land and access land in one go. Free: 3 checks a day.