In general production companies in the UK, including the BBC are not too fussy about the precise format of a script. In Hollywood, by contrast, as far as I am aware they like scripts precisely formatted to match the particular show and there are slight variations over time, which they use to identify scripts by the IN-Crowd as opposed to newcomers.
The UK people are usually happy to read a script & judge it on its writing merits, but it should look like a script and not your own concept of what a script should look like. Consequently it is bad manners to invent your own format.
There is a clear distinction between submission scripts (that provided by the writer) and a production script (that produced by the production team and actually used during the filming/recording). Production teams will transform or retype a submission script into their particular production format when production starts and it will no doubt have many revisions and changes made during the production phase.
Script formats are traditional, they date back to the days before desktop computers, when all scripts were typed on typewriters and copied with spirit duplicators or (later) photocopiers.
Broadly speaking there are four classes of script format, each with their own merits.
Film Format - For SINGLE CAMERA recording
(B) Studio Format - for 3 (or more)CAMERA Recording
(C) Stageplay - for an audience (no cameras)
(D) Radio Plays - Microphones only no cameras.
During production, script changes are normally issued as replacement sheets, using different coloured paper for revision1, revision2 etc. This was originally done to cut down on re-typing and copying, but tradition carries through to modern times when it is less essential. During production each team member as well as the actors will have their own copies and will have marked them up for their particular jobs. Issueing only changed sheets means that they only have to transcribe their personal notes of the changed sheets not the whole script.
Film format is used for almost all drama and near drama scripts, especially exterior scenes etc. It has CHARACTER NAMES and dialogue in the centre of the page with space on either side (presumably for actors to write in their notes) the stage directions are wider; the full width of the page. Producers like to think that each page will produce ONE MINUTE of finished film.
For writer's submission scripts in the UK, Film Format can almost always be used. [but it would be wise to ASK before-hand]
Generally drama and exterior scenes are shot with one camera. For different camera angles the actors repeat the acting over and over again with the camera moved between shots [It can be quite a boring job being a film actor 
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Scenes are not filmed in sequence, they are filmed by location. Thus all the scenes at a given location will be filmed one after the other and then the whole team moves to a different location and does all the scenes there and so on. So in addition to the script, the production teams have numerous other bits of paper for: shooting schedules, continuity notes etc.
(B) For Studio sitcoms, with a live audience, the scenes are shot in sequence because it would otherwise be completely boring to the audience. External scenes are done beforehand and shown to the audience in sequence on overhead monitors. Scenes are only repeated if it was a bad take, each take is checked briefly before the next scene is recorded. The studio will normally contain 3 SETS, which are like rooms with one wall missing. The audience and cameras can see what the actors are doing in the room through the missing wall. Though the sets might represent places far apart in the story, they are actually right next to each other in the studio.
Audience laughter gets tired after the same scene is repeated umpteen times so the single camera technique can't be used with a studio audience, so at least three cameras are used simultaneously to provide all the camera angles needed and some very skillful people up in the control room cut from camera to camera on the fly to get the finished recording. Some cameras may also be continuously recorded to provide material to be re-edited into the final cut to cover up bloops made during the recording. 
Shooting instructions for 3 cameras take up a lot of room so the production script for a studio sitcom has a lot of space allocated to it. Basically the whole left hand side of the page is reserved for camera and sound actions and the actors script is in the right hand half. [Example http://www.datahighways.net/dhl/downloads/w8/byteback.pdf]
If you are writing for a studio sitcom there may be a small advantage in writing in Studio Script format, because the producers will be more used to seeing their scripts in that format. However it will use more paper. The production team will almost certainly re-type it into their own production software, so you don't have to be ultra fussy.
(C) As far as I can tell there is no specific format for stageplay scripts in the UK, though I gather that in the USA, they use something very like Film Format. So for UK stageplays you just basically need something that looks good and is easy for the actors and director to read. When I was choosing which of my 14 format Templates in the Scriptwriters Toolkit should be the free sample I decided to make it the nicest of the stage-play formats that I had prepared as it would then be completely zero cost to school-children who might wish to write a play for production in class or as a school production.
(D) Radio Scripts used to be just one long continous script, because scene changes are perceptible to the audience only by the changes in ambient sounds produced by the sound effects people, but more recently the BBC format as indicated by Scriptsmart has the scene headers in place. Perhaps this makes it easier for the script readers in Writers Room. The basic requirement for a radio production script is of course something that can be read easily without confusion while speaking into a microphone.
A young lady called Sally Farmer used one of my radio templates to write quite a funny radio script about pidgeons, which alas has not been produced, but is shown as an example on my website. http://www.datahighways.co.uk/dhl/downloads/w2000/PigeonKindR1.PDF
There are other sample scripts on my website, but the rules of this forum say that I'm not allowed to give you a direct link to the page, so you will need to do a teeny weeny bit of research to find the right page. 
Have fun.. "Break a Pencil"
