UK IFR definition
A lot of folk get confused (rightly) by UK IFR definition and requirements. Of course if you mean within Class 'A' airspace then you are talking about the equipment lists as specified in the ANO.
However, the ONLY 'instruments' you need in the UK for IFR in Class 'G' are an altimeter (for telling if you're 1,000' above an obstruction) and a compass (to tell what course you're on with reference to said obstruction)
UK IFR definition outside CAS has NOTHING to do with flight 'by sole reference to instruments' as it does elsewhere and you might sensibly think it should here, too.
TheOddOne