bought a sony 46 inch with a stand + dvd player yesterday,
i was shocked and pleased with the quality of Virgin HD on demand but when i went back to the normal channels sitting back of the room, i could easily see all these blocks of pixels, the quality was terrible.
can HDtvs not support scarts or any signal that isn't hd?
it just comes out completely terrible

Sony: 46W3000

The bottom line is that you are using a very demanding display (as are all flat high definition flat panels) and standard definition source material is simply not upto the job of making the most of the screen.

The problem is that a SD source has to be enlarged (scaled up) buy the TV (or DVD/STB device) to the screens native resolution and since there is not enough picture information there to begin with the missing bits have to be guessed at.
Unfortunately the bulk of SD broadcasts (all not just from VM) are far below even DVD standard (which looks pretty good on a flat panel) and unless you realise before hand the difference between a CRT which was made for SD and a HD Ready LCD/Plasma which was made for HD then you can be in for a shock.

Of course a TV has many tweaks to optimise the display for SD material and a trip over to the AVF thread for the TV may help.

Also it's VERY important that you don't watch via composite video, use RGB, or HDMI - I'm presuming the V+ has HDMI as it has a rudimentary HD service.