SnowPlowing is easy !
I am sure that LHR has plenty of lorries etc. used for other things that could have a snowplow mounted. So instead of paying for the whole truck you just pay for a plow that is removable and easy to store. Then you train several dozen operators for the unlikely event and away you go. Additionally you could contract with a trucking company or heavy equip company to be on call. This has proven to work in other airports where snowfall is a rare reality.
This does not cost millions and should be a requirement if you have any possibility of snow during the year. It is afterall a safety issue.
Besides what else do all those landing fees go to pay for !!
However you would need to have Type IV de-ice available not just Type I.
Cheers
FG