I would have suggested a tyre problem but if swapping with the rear didn't make any difference the only part that rotates with any ammount of load on it is the wheel bearing, given the mileage I wouldn't have expected it but its the most likely cause.

If by wheel alignment you mean tracking, that will not normally cause a car to pull to one side, incorrect camber angle will but that's unlikely to be wrong unless some damage has occured. Unevenly worn tyres can cause bias to one side but swapping them over should at least have changed it.

I have spun the wheels up by hand and there doesnt seem to be any resistance, noise or vibration so if it is a bearing it is only causing a problem under load which I would expect to get worse when I steer as this would either lighten or exaggerate the load on the dodgy wheel. I would be tempted to just get the bearing changed but its knowing which side is the problem. One of the mechanics I spoke to said we could try to spin the wheels up on his rolling road to see if we could replicate the noise but I still think distinguishing the side is going to be a struggle.

Nothing like that, I had to take the undertray off as when removing it for a service some of the bolts sheered off and havent had it fixed. All wheel arch liners are secure. Its more of a rhythmic rotation noise that increases and decreases with speed.

I checked all of the boots and couldnt see any tears, they looked in really good condition actually. There was no grease on or around the boot area to suggest that they had leaked at any point either. This is why the problem is so annoying as I have checked everything I know of that could cause the problem and it all appears ok so maybe it is a bearing that isnt giving the usual symptoms of failure. It sounds like a bigger rotation though so im still thinking a tire problem as bearings being smaller usually rotate quickly making a very fast noise whereas the noise I have is slower, probably about 2 or maybe 3 "womps" a second when doing about 40mph. I would still be suprised if a bearing had failed after just 50,000 miles but I have heard of it happening so maybe I am unlucky, either way I still cant hear what side it is to even think about replacing.

Yep, did this last week. Problem still present and sounds like the same area......annoyingly! I had hoped it would make some sort of change but it hasn't