Now first things first, I'm not a lawyer. I certainly won't be paying your fines for you, however I did find some things on tinterweb that will help those "do we need GB stickers" type questions.
Firstly, you would do well to read section 8 in the DVLA brochure INF104, _Vehicle registration __numbers and _number plates. Section 8 is labelled "The Euro symbol on a number plate", and it refers to "The symbol must meet the EC Council Regulation 2411/98". The Regulation can be found here, In the ANNEX off the regulation it explains for two-line number plates, "Where the dimensions of the blue background have been reduced for registration plates taking up two lines (see model 2) and/or for registration plates intended for two or three-wheel motor vehicles, the dimensions of the stars and of the distinguishing sign of the Member State of registration may be proportionately reduced."
It still needs to go on the extreme left, but makes no specific on the proportions by which it needs to reduce. It does presume by the example that it would go on the first line though, not the second but it makes no written specific as to which line.
This looks like you can buy one of those 51mmx23mm blue stickers with the circle of stars at the top and GB written at the bottom (in either white or yellow) and stick it on the second line of your number plate, as long as it is on the extreme left.