Oh really, they did it so they could save money, however saying that the special film effect must have set them back abit so really the scheduling change was unnessasary in my view I think.
The film effect doesn't inherently cost any more when you shoot in HD. Unless you use VERY cheap cameras, most HD cameras allow you the choice of running at 50i or 25p. If you shoot at 25p with a 1/50th second shutter you get the same motion rendition as shooting on film pretty much (which shoots at 25fps with 1/50th second exposure if you use a standard 180 degree shutter)
Pretty much all single-camera drama is graded in post, and even some multi-camera stuff is these days, so the "look" in terms of colour balance and exposure is also cost-neutral. (Though some low cost multi-camera soaps won't go through a grade, they'll rack to a neutral look in-studio - and that is cheaper)
Lighting for the film look MAY cost a bit more - as giving stuff a flat uniform lighting effect might be a bit quicker and easier, particularly in studio when you first light a set, or on a set you only use once. However lighting for a more contrasty, pools of light and shade, effect - which is seen by some to be more cinematic, may actually be quicker and cheaper if you know what you are doing, particularly on location, and may be pretty much cost neutral on a set you use a lot.
You could argue that moving The Bill from SD to HD production is a cost increase that wasn't needed - but anyone shooting drama these days, particularly if they want to sell it abroad (and The Bill is popular in Aus, and I think NZ) has to consider HD - as it is now the norm in many territories, not just a "high-end" thing. The UK is moving quickly to HD being the norm as well - though ITV are lagging behind the BBC, C4 and Sky in commissioning HD content. (Probably because the revenue benefits are less marked for them)
