I am trying to replace an old light with a new one. The lighting circuit is two old grey cables with red and black wires and no earth. The new light is brown/blue and earth. The existing light has both reds on one terminal and the two blacks to two separate terminals (screws).

How do I connect up please?

what type of light fitting is it you have bought, plastic or metal?

Metal I am afraid. actually prob about 15 years old!

if it's metal you must provide an earth wire to it, failing to do so can be dangerous and we cannot explain what to do until you assure us you have put an earth in.

using an old fitting is not a good idea anyway. the terminations within the lamp holder dried up and crack. for the sake of about £3.00 you can buy a new plastic one.

more to the point, if your wiring is pre-earth then you are seriously in need of rewiring. changing light fittings is probably the least of your worries. i would guess your wiring is around double the recommended age of rewiring.