2. Is it feasible to get there in a SEP (non FIKI) from NE England in winter?
Sure - depends on the weather
3. Is it feasible to do with an IMCr rather than an IR? (specific day of arrival not being a massive issue - within a day or two anyway).
As above
I think, as you are talking VFR-only, you have about a 25-50% chance of doing the trip on a specific day.
IFR will improve it somewhat but not as much as one might expect. In warmer temps, it improves things to maybe 75% or more, IF you can land on an IAP.