Was a supplementary agreement a separate "construction contract or, was it just a variation to the main contract?
Links
[1] http://fenwickelliott.uk/sites/default/files/legal_briefing_5-2007.pdf
[2] http://fenwickelliott.uk/sites/default/files/legal_briefing_1-2007.pdf
[3] http://fenwickelliott.uk/sites/default/files/legal_briefing_2-2007.pdf
[4] http://fenwickelliott.uk/sites/default/files/legal_briefing_4-2007.pdf