There is a JAR rule that said something along the lines of:
A pilot without an IR can fly under IFR, provided that they remain in VMC if it is required to comply with a technicality.
However this rule was never copied into Irish law as far as I can see, hence an EI reg aircraft can't fly at night in the UK (except SVFR in a control zone).
Might be worth looking to see if that rule was copied into Belgian law....if it was, it would give you a way to fly under IFR without an IR in UK airspace.
dp