As the title says Buy 3 pack gu10 (240V, 50 watt) get one three pack free! A Rated.
Just be careful though as there are two versions = 1,000 hour and 2,000 hour.
The 2,000 hour ones are obviously the one's to go for.
These are dimmable.
The 1,000 hour ones are £4.99 for three at argos OR 5 pack for £9.85 @ screwfix for 2,000 hour ones.
Also they had some which were rated at 12V for 3x @£3.99 B.O.G.O.F (also by Philips sorry don't remember the wattage or pin type only remember they were the same shape bulb as the GU10, possibly mr16's?)
They were on the next shelf down.