Turn on your sink taps (closest to the shower) and guess the same amount of water flow as your shower exudes and see if it does the same.  It may be that your local authority has reduced the pressure in the area as so many consumers are hammering it over the holidays.  This little test may confirm that.

Secondly ensure your crutch valve where the water enters the house is fully on but beware cos it may blow the bottom out of your kettle.  These simple tests can confirm that water is there and enough to create an effective shower.  If they pass then look at the shower itself.

Thanks for the replies lad`s but after an hours nagging off shmbo i traced the problem to the showerhead. The rubber nozzles inside the plastic head had became displaced and were blocking things up.
It`s amazing how a bit of nagging get`s you off the couch instead of my plan to look at it tomorrow LOL.
Thanks anyway.