Chuck - in the UK you only need an IR or an IMC rating to fly in Class A to E (IR) or Class D and E (IMCR) when compliance with IFR is mandatory - such as in IMC. If it's gin-clear VMC and you only have a plain vanilla PPL you can, if you wish, fly under IFR and are then only required to observe the min. height and quadrantal/semi-circular rules. You don't need anyflight plan at all! All UK night flying is under IFR, so if you don't have an IR or IMCR, then to fly in a Class D CTR you would have to fly under Special VFR. Same goes for any flight in Class A airspace; without an IR you'd have to fly SVFR.