IO540
A few misconceptions in your piece, but nothing major.
When you file a FP to Eurocontrol you get an airways squawk allocated.
If you are saying Eurocontrol issue a squawk as part of some global system, then no, you don't. The squawk will be issued by an ATC agency when the IFR plan is 'activated' with them. This could be carried out either as a pending flight (when it is issued by the flight data processing system, along with the flight details, to the ATC unit 40 minutes before departure), or it could be a flight coming from a non ATC airfield and allocated when the IFR ATC unit ask the system for a code.
When you get airborne with this squawk, and it is picked up by one of the radars, the IFR FP pops up on their screens, and then when you call them up they know about you and send you off into CAS, to your filed level/route etc. This is what happens when you fly from say Bournemouth to Berlin at FL150. Very smooth and simple.
It's not quite how it happens in the UK en route IFR system. For IFR departures from airfields with ATC of any sort, a departure warning will be given and an IFR clearance issued, either as an individual co-ordination with the Area Control centre, or as a 'freeflow' departure following a standard route and level with no prior co-ordination required. The Flight Plan will already be in the Flight Data Processing system (along with the allocated SSR code) but will not yet be active. Once the aircraft gets airborne, the flight is activated in the system, either automatically or manually, and all controllers downstream are then passed electronic flight data on the live flight with appropriate levels and times for waypoints calculated. No 'IFR FP' pops up on the screen, and all that will happen is that any aircraft displaying the allocated squawk will show on the radar screen with the allocated flight callsign and route data. For aircraft departing from a non ATC airfield, then the SSR code will be allocated to the flight over the RT and the plan activated manually in the FDP system. Setting the SSR code allocated will not do this automatically in the UK system.
But if you never go up with that squawk (because you filed an IFR FP but you never picked up the airways departure clearance) that squawk will never be seen, and after 30 mins past EOBT the FP gets dumped.
Not true. The FPL is not automatically cancelled, although the assigned SSR code will be dropped after a time parameter (around 4 hours I think) and a new one will have to be requested. The Eurocontrol IFPS system will also assume that the flight has departed unless it is told otherwise, but this is for air traffic management purposes rather than ATC purposes. No live data will be transmitted for the flight by Eurocontrol and it will remain within the ATC FDP system until the end of the day, or until manually removed.
If you depart on an IFR FP from an airport capable of airways departures e.g. Bournemouth and the FP says 2000ft then Bournemouth tower will look at this FP and will realise you are just an amateur playing low level (probably an IMCR training flight where the instructor got you to file an IFR FP for fun) and is not going to pass you the airways squawk because they can "obviously" see that you are not heading for any airspace run by LC.
There will be no Airways squawk ever allocated automatically by the FDP system unless the flight is planned to enter airspace under the control of one of the UK Area Control Centres (ACC). Such flights will automatically be inserted in to the FDP system when the FPL is received from IFPS, with manual correction being applied as required. If you are an 'amateur' IFR pilot (very harsh to generalise people with that I think ... some professional GA pilots and airline guys I have experienced could also be described as amateur), on a flight planned to stay outside the Airways system, then the ACC will have a copy of your plan in their domain, but it won't have been input to the FDP and therefore the sector ATC staff won't be able to directly access your details, nor will any processing on your flight take place.
If incidentally you did later try to get that flight elevated to airways it won't work because it got dumped...
It won't have been dumped, but it takes time for the sector to get support staff to find the plan and input it in to the FDP, along with any changes you have asked for in terms of routeing and level. The priority will not be a high one.
So what is the point of filing an IFR FP OCAS?
None really. No enroute unit is going to see it, and because it went to Eurocontrol it is likely (??) that even the destination ARO will not get it (because it gets dumped 30 mins past EOBT if the allocate squawk is never seen).
If it is filed IFR, then the ACC will get it if it is within airspace or on routes that they have notified Eurocontrol as being interested in. On receipt of a FPL in IFPS, it normally takes only a minute or so for the distribution to take place and this is not dependent on a flight being activated, so there is no 'dumping' issue. The FPL will be sitting at the destination airfield with your planned EOBT and elapsed time en route, but is not live. Local procedures will then dictate what they do with that plan and whether any action is taken if you don't arrive at the planned ETA. If it is relevant, then the FPL will also be input to the UK en route FDP system and will sit as a pending plan awaiting activation. For a UK departure, the pending plan will (generally) be distributed to the first ACC sector 40 minutes prior to the planned departure, along with the allocated squawk. If your plan has not been activated by the end of the day, your details will be discarded by the sector staff and the FDP system will drop your pending plan out of the system.
An airport operating the IFR rules properly (typically, one in Class D) will not let you depart VFR into sub-VFR conditions, so there you have to do an IFR departure, and the existence of an IFR FP will be irrelevant.
They might let you depart Special VFR though.
The only advantage of filing a FP (VFR or IFR) OCAS is that somebody can dig it out if you crash somewhere, and go looking for you in hopefully roughly the right area. But, in the UK, somebody still has to raise the alarm - a FP is automatically closed even if you never arrive!!
The UK has the 'responsible person' method. I think this is far better than depending on parameter times and flight plans, as someone will be actively looking out for you, and will know who to contact if you don't turn up. You can of course ask the parent ATC unit to be this person on your behalf.