I always thought that there was something written into the Railways Act which was an exemption from noise abatement regulation.
Quote from Direct Gov
Railway noise
People living close to railways might be affected by high noise levels. However, there are no legal controls unless the noise is caused by a new railway affecting your property. In this case, you might be able to get a noise insulation grant.
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also this taken from Hansard 28 Feb 1998
It discovered that section 122(3) of the Railways Act 1993 gives all rail operators a statutory defence against the Environmental Protection Act. Those who take action against the rail operators have to prove that their operations and actions were, in the words of the section, "totally unreasonable".
So from this we can see that the Railways Act gives an exemption from the Enviromental Protection Act. So it looks like all of those noise abatement orders are just worthless bits of paper......