I don’t think I agree with some of the above. In my opinion it does need planning permission as it is not built in materials of similar appearance to the original house – ie brick. See condition A.3(a) of
http://www.legislation.gov.uk/uksi/2008/2362/pdfs/uksi_20082362_en.pdf
It should also have building regs approval. L1B 3.15 & 3.16 state when conservatories are exempt, ie this does not define what a conservatory is, just which conservatories are exempt. As far as I know to be a conservatory it needs 75% glazed roof and 50% glazed walls. Even if this rule has been redefined I can’t imagine an extension with three windows is ever going to be considered a conservatory.
I think the 2m that you refer to is a building regs issue, not planning. The building is made of timber so all the external walls are unprotected areas. If the flank wall is between 5.6sqm – 12 sqm (which it is) it must be 2m min from the boundary (Building Regs B4 Diagram 22)