Just to recap (for myself
)......UK VFR minima in class G (assuming class G) specify minimums of 1500m vis, clear of cloud and in sight of surface below 3000' and 140Kts. Above 3000' its 5km vis, 1500m from cloud and 1000' vertical seperation from cloud....
So i suppose in theory you could depart VFR and remain "clear of cloud and in sight of the surface" and not break the 500 or 1500' rule.
As mentioned, switching between VFR and IFR outside CAS in the UK is a sinch, you just do it. Depending on why I wanted to fly would determing whether I depart IFR VFR or at all. If travelling A to B, I would file an IFR flight plan (icing permitting) and depart IFR. If I was just going for a jolly, I wouldn't go, as "Max VFR" (named after a friend of mine, who specialized in dodgey VFR
) is highly dangerous in my book.
Departing IFR, and filing an IFR flight plan would probably help in getting a RAS, though I am not sure on how the system works with regards to routing IFR flight plans. Probably a LARS unit wouldn't get a copy. Every time I've pre-filed though, it certainly seems easier to get a RAS. Also pre-filing seems to help getting airspace transitions, and you won't get a routing change unless you are inside CAS and they want to change your route for some reason. ATC cannot route you through un CAS, and to enter CAS you'd have to have an IR and fly the airways. When transitioning Class D airspace, you'll be provided Radar Control service, where you're essentially given vectors to fly, so no big deal there.
Probably the worst thing you could do in this situation is depart VFR, then switch to IFR once airborne especially if you then want to negotiate CAS transitions. At least when you pre-file, someone knows you're going to be there.....
Cheers
EA
PS Depating a field with no IAP is no problem. Just remember you may not get back in again in an emergency, so it could be considered un wise unless you have an alternate nearby, or have made up your own GPS procedure