Hi Dave,
This is a show I used to frequent Myself from it's days at Alexandra Palace, I do recall it moving from there to Wembley and of course to Olympia. I do believe it is still held in January each Year, see the weblinks below...It has returned to Alexandra Palace for 2008. An ideal location, as it is only 9 mins on the train from London Kings Cross and it is right next to the train station when you get there.
http://www.londonmodelengineering.co.uk more info is on the same site as follows:
http://www.meridienneexhibitions.co.uk/
I used to spend many happy hours (and a few bob !!) browsing at these shows and enjoying all the new models and kits coming out...even coming home with the odd one here and there...Impulse buys !!
Regards.....Mark.