A strong performance yesterday on the Nasdaq saw UK stocks gain on opening this morning. But it was a short-lived momentum as the FTSE dropped 0.5 per cent, and the Techmark dipped 0.2 per cent, in the first hour of trading.BT dropped 3.10 per cent to 554.5p, after an initial gain, following news that chairman Sir Iain Vallance is to resign. Marconi fell just under one per cent, after opening up 1.8 per cent at 337p. Arm Holdings managed to hold on to its 2.7 per cent gain, with Autonomy also rising after announcing first quarter results that met reduced expectations. In Frankfurt Siemens fell 2.6 per cent after reporting reduced profits and job cuts in second quarter results announced today. Alcatel shares fared better in Paris after the company posted a 21 per cent profit increase in first quarter sales.