There are no rattles or clunks , whines or grinds . Just a great increase in road surface noise particularly at motorway speeds . The tyres are the originals and nearing the end of the life , could that be the cause . Dipping the clutch , knocking it out of gear and freewheeling at high speeds makes no difference . Any ideas ?

tires, alignment, ear blockage, l would guess even though they r worn at 47k miles they do not make noise unless they r out of alignment.

Easy to hit a curb too hard. or a bad pothole. Since this something new, l assume, u should not be hearing any noise from tire wear. Being out of line could cause a sudden increase in a little more noise but old bald tires r not noisy, they r just dangerous at high speed.

l am sure of it. & l have repaired a lot of cars & learned about tires from nascar fans a few drivers. Old tires just do not make more noise.

you still have the original tyres after 47,000 miles?!?!?!?

I'd guess they would be a good place to start, if they are below proper tread you stand a really high chance of losing control of the vehicle due to blow out or not enough grip to stop.

The tyres look a good place to start. If they have very little tread on then more rubber will be contacting with the road and thus causing more noise. Get the garage to check your wheel bearings and steering and suspension for wear while the car is on the lift also.

It could well be your tyres. When tyres are new the tread blocks are deep and flexible. This flexibility reduces the scrubbing effect of the tyre on the road. When tyres are heavily worn down the tread blocks are much shallower and therefore have less movement. Because of this the tyres will tend to scrub the road surface instead of flexing over it, increasing the road noise.

sounds like you might have a out of shape tyre [usaly on the back] or you have a wheel bearing gone. if the note of the noise changes when you corner then its moor likley to be the wheel bearing.

definitely tyres replace them and you will feel and hear the difference.

It is a Peugeot. Deal with it, man.
Now, for some practial advice: find yourself a long, soft, dirt road or driveway, get up to speed and press the clutch and coast. If you do not hear any noise then it is your tires.
l had to do the same thing with one of my cars -- road noise was so loud l thought the rear axle assy. was going out. Turns out it was just noisy Khumo tires.