-
a local building site (in response to sausagefingers) is unlikely to deliver.
what's wrong with Travis Perkins? or try a local timber merchants:
http://www.yell.com/s/timber+merchants-islington-central+london.html
I would say that 2x1.5 is an odd size - many places will cut down to size for free. standard sheet sizes are 1.22x2.44m. you can get 3.05x1.525m but stock/type is more limited.
mrs_com has a project in work that needs a couple of sheets of ply or OSB (basically flat sheeting that can be painted and will stand by themselves against a wall) about 2m by 1.5m each or thereabouts.
Where in London would she be able to order this and have it delivered to Islington. Pick up/collection is not an option.