A discontinued model from Crucial, but about the cheapest I've seen for a new, brand-name 256GB SSD after the recent price increases. An end-of-line offer, in-store only I think. They also had a few 512GB MX100s earlier in the day for < £100 but they all went - other Office Outlet's (used to be Staples) might have them.
Edit: The store is no longer Staples - it's been renamed as "Office Outlet"
and as of 2017-03-02 12:55 the SSDs are still there.