From 25th May 2007 for motor vehicles categorised as M1 (a passenger carrying vehicle not exceeding 3.5 tonnes and not more than 8 passengers) or N1 (a goods vehicle not exceeding 3.5 tonnes) it will only be legal to manufacturer and sell bull bars that comply with EU Directive 2005/66/EC.#
It will be illegal to manufacture and sell bull bars that do not conform to this legislation punishable by a maximum penalty, to be imposed within the UK, of 12 months imprisonment and/or a fine of £20,000.#
Operators of vehicles already fitted with these devices will not be affected
Basically there is nothing that says you can't fit a bull bar that was manufactured before the legislation was introduced. Might need to look into more detail to see if that is true for post 2007 vehicles.