This is an IKEA Double (as opposed to standard UK double) MALM Birch bed-frame. IKEA double frames are slighly larger than standard UK ones.
It doesn't come with a mattress.
A standard UK mattress would fit in the frame - there would just be an inch or so gap at the side and a few inches of gap at the end (or top).
It will be available for collection from week commencing 23rd March.
It will be dismantled prior to collection.
IKEA Double Bed Frame (Towcester NN12)