Battle of Britain plotting Hostiles

Hi everyone, I'm new on the forum,
I have a question concerning the plotting of targets in operations rooms during the Battle of Britain. When they were detected approaching the English coast, they were classfied as 'Hostile' and given a number. I know its an odd question but what was the system for giving them numbers? I don't think they were randomly classified 'Hostile 2-1'. If anyone knows anything about target plotting please let me know!
Thanks all!
regards,
Celticmarine

Very basically, all plots that were not positively identified as 'friendly', were given a number, starting at, for example, 'Hostile 01'. This would include all plots right around the British coast (including Scotland, not just England) at this period, mainly on the north, east and south of the mainland British Isles. (later, this would include the west coat also).
This was a very simple, but effective, way of filtering the info from all of the Chain Home stations, which stretched right down the east side of the mainland, and around the Channel to the west, and plots were numbered according to when they were first plotted.
For example, 'Hostile 15' might be an unidentified aircraft (or formation) approaching the north east coast of Scotland, whilst 'Hostile 03' might be similar approaching the south coast of England, across the Channel. The location, perceived threat, possible destination etc, might therefore 'prioritise' the subsequent action/reaction of Fighter Command, passed on the the relevant Group.
The 'Hostile 15' could, for example, turn out to be a civilian flight, from a perhaps neutral country, or maybe even a returning RAF aircraft, off track etc etc, and would be placed, or removed, from the plotting tables at the relevant Group and Sector Controls once positively identified.
Hope this makes sense !

Indeed. The system did not always however operate as smoothly as in the movies.
During pre-war (June 1939) exercises reports from inexperienced member of the Observer Corps led to an "utterly chaotic" display on control room maps. Dowding ordered that raids reported by the Observer Corps be ignored unless already reported by radar. This goes against the common perception perpetuated in some films. He also created a "lost property office" as some raids simply disappeared as they crossed group or sector boundaries.
Dowding was not a fan of the Royal Observer Corps. He once wrote,regarding an invasion,which incidentally he didn't think was possible,that "The first news the Observer Corps would get of the invasion would be in the morning papers."
There was much caution about over reliance on radar. In late 1939 Park wrote to Dowding complaining that his group and sector controllers were regarding radar as "totally reliable black magic" when it was not. Clarification was issued. In March 1940 Dowding wrote that radar was "very capricious and unreliable,but is better than nothing,as being the best evidence we have for what is going on over the sea."
This just leads to an even greater appreciation of what Dowding accomplished. Against all the odds,human and technical,he did create a coordinated air defence system which,combined with a muddled and ineffective strategy on the part of the enemy,saved our bacon.
Arthur "Bomber" Harris wrote of Dowding that he was "the only commander who won one of the decisive battles of history and got sacked for his pains." I can't say fairer than that.
He did win it too,despite modern revisionism. In both August and September 1940 the luftwaffe lost about 25% of its fighter establishment and about 20% of its bomber establishment. These figures were nearer 5% in July.
They were also running out of aircrew. On September 14th 1940 Bf109 squadrons had only 67% operational ready crews against authorised aircraft,for Bf110s it was 46% and for all bombers it was 59%. With the exception of the Bf110 figure these numbers fell in the next weeks too.It couldn't continue like that.
Dowding said before the battle that he only had to survive until November and he did far better than that.
Cheers
Steve

Thanks that helps lot!
Do you know if they started plots at a certain number? How did they get up to 2-1 or 1-1?
Thanks!
Regards,
Celtic