The Land Compensation Act dates from 1973. Any developer wishing to enlarge an airport should be well aware of it, and should have factored it into their consideration when deciding whether or not to start the building works.
It is possible that the 1,200 households are having a go to see if they can get anything - but if you had bought a house near to a very very sleepy SEN in 2005, you would have had to be very imaginative indeed to foresee it undergoing major redevelopment and be handling almost 1 million passengers annually by 2013.