At the risk of splitting hairs ‘ol chap, that is not “legislation” just guidance on the law relating to marine distress flares issued by the Maritime & Coastguard Agency.
A quick bit of g00gle-fu threw up various threads on forums where yachty types were getting blazer buttons in a bit of muddle over this but the closest anyone could come up with was the Merchant Shipping (Distress Signals and Prevention of Collisions) Regulations 1996.
http://www.legislation.gov.uk/uksi/1996/75/made
Regulation 3 sets out the responsibilities of the masters of vessels in relation to distress signals. However, at the time I was disposing of my old signal flares, rather than being the master of a ship, I was leaning out of a window in a flat in central Brum, which is about as far from the sea in the UK as it is possible to get while the sky was lit up with fireworks from bonfire night, Diwali celebrations and (probably), drive by shootings.
Happy to be pointed in the direction of specific legislation relating to letting off flares on land and I’m sure there are potential public order offences if the flares are being used dangerously (IIRC a few years ago someone let off a flare at a football stadium and killed someone in the opposite stand) or to cause a nuisance or to deliberately hoax the emergency services, but in the real world, letting off what is basically a firework during a firework display in the middle of a city 50 plus miles from the sea is unlikely to be of interest to anyone in authority even if they could tell the difference between a distress flare and a Harmonious Mega Scarlet Interplanetary Sky Shredder Delux rocket from the cornershop.
If the OP can find someone to take his old flare away for disposal then great but if not, as he is a long way from the sea or any mountain or moorland and the countryside is as soggy as it can get, next week would seem an ideal opportunity to get rid of them and personally, I would feel far safer letting off an out of date distress flare than a firework.
TBH rather than being worried about the firework police, the sheer number of unnecessary apostrophe’s (
) on this thread has probably got the grammar police careering around the country with their blue’s (
) and two’s (
) on to execute multiple arrest warrant’s (
).