Uxbridge is not under the flightpath and wouldn't be with 3/4 parallel rwys.
But doesn't the constituency also include South Ruislip (and Northolt Aerodrome) ?
And don't some of the flightpaths in options included in
http://your.heathrow.com/wp-content/...Assessment.pdf
show curving flight paths around Uxbridge which would impact on South Ruislip ?