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"What they want to do here is a warning to anyone else: if you think you have got green belt and you think it will be there forever, say goodbye to it."

In a yellowing wheat field, next to an oak tree, we are standing on the front line of huge changes to London's green belt.

This is 85 acres of green belt on the edge of London between Potters Bar and the South Mimms service station.

Ms Albrecht says the data centre will devastate the green belt here.

"Whilst technically designated as green belt, the land performs poorly against the purposes of the green belt, being adjacent to South Mimms Services and the M25, and benefits from being set in a valley, meaning development can come forward in a sensitive way. The site can therefore be characterised as grey belt."