Many thanks for all the information!
2. The dwellings hereby permitted shall be constructe to achieve a minimum Code for Sustainable Homes Level 3 and achieve a minimum of 1 credit under category Ene1 - 'Dwelling Emission Rate' in accordance with the requirements of The Code for Sustainable Homes: Technical Guide (Version 3) November 2010.
...and...
4. The dwellings hereby approved shall not be occupied until a Code for Sustainable Homes 'Post Construction Stage' assessment has been carried out in relation to the dwelling and a 'Final Certificate' has been issued... etc
I was not so concerned about meeting the sustainable home code, but I had planned to occupy the site while working and this implies I cannot occupy the site until after it is signed off, unless I seek a separate permission. As the code may now have been superseded, would that null and void that whole condition?
Good to know.
No real uniformity of size, and only loosely in style, but we're after something that would be generally in-keeping.
So first steps - check that the council are happy with 'material commencement' and informally discuss changing the permission to something similar but smaller.
Then, if everything looks good, secure a Lawful Development Certificate and engage a planning professional to submit revised plans.
Finally, attempt to purchase.