Disposing of your expired Lead Acid battery needs to be done according to UK law. Battery acid and other components of Lead Acid batteries are toxic for the environment and cannot be thrown away as general waste.
Here are a list of websites and places you can visit as relate to Lead Acid Battery Recycling in the UK.
1 ) Your local municipal waste disposal facility. Here items like batteries can be properly classified as hazardous waste and disposed of on your behalf.
2 ) Your local tyre and exhaust center will often collect waste scrap batteries on behalf of the public and send them for recycling.
3 ) Visit http://www.recyclenow.com where there is a UK Postcode search tool.
Please Note that whoever you hand your old battery to has to carry hazardous goods certification. If they don't then you will both be breaking the law and risk being prosecuted under the Carriage of Dangerous Goods act or a similar environmental law. Additionally by doing so there may be no particular guarantee that the scrapped battery will be dealt with safely and with the environment in mind.