Spray paints are subject to strict laws in the UK. Selling to under 16’s is against the law in an attempt to clamp down on the graffiti problem plaguing the country.

According to royal mail the delivery of spray paint aerosols are also subject to restrictions.

“Aerosols including deodorants, body sprays, hair sprays, shaving and hair removal creams, medicinal aerosols for prevention or cure such as flea sprays, etc.)
Valves must be protected by a cap or other suitable means to prevent inadvertent release of the contents during transport. Aerosols must be tightly packed in strong outer packaging and must be secured or cushioned to prevent any damage. Volume per item must not exceed 500ml. No more than two aerosols can be sent in any one package. An ID8000 label must be applied”

https://business.help.royalmail.com/app/answers/detail/a_id/898/~/restricted-goods—uk

https://en.wikipedia.org/wiki/Aerosol_paint
http://spraytechnologiesaerosols.com/