In what looks to be the result of rumour feeding on itself and dealers seeking to fuel a bit of business when trading is so thin, Plessey Co Plc shares had put on ninepence to 167p by lunchtime yesterday and Reuters added fuel to the flames by putting out a note on its newswire. Needless to say, the name that came top of the list of possible predators was Siemens AG, but Siemens, not doubt a little wearily by this time, issued a denial. Other names out of the hat were AT&T Co – as a substantial defence contractor, Plessey is unlikely to be allowed to go to a foreign firm; STC Plc – a possibility in the medium term but right now it has to sort out its new business arrangements with Northern Telecom Ltd; Thorn EMI Plc – it still has enough problems of its own and is surely not ready to take on any new ones. The other name mentioned was Hanson Plc. Well yes, it was that kind of day in the market…