Wickes are doing a 3 for 1 deal on their various thicknesses of loft insulation.
In store only and I think just until end of September.
I needed 170mm thick and this is £29.97 per roll (but they do other thicknesses depending on if you are looking for base layer or top.
Details for this roll:
* Covers 8.15m2
* Significantly improves energy efficiency
* Glass mineral wool
* Easy to divide
* Suitable for 600 and 400mm joist and rafter spacing
* Compressed for easy handling
They often have bogof on this but in this case it is 3 for 1 so I can do my loft for £30 instead of £90 - hope it helps others!