BRITISH Airways chairman Sir Colin Marshall has begun quietly hunting for an Asian airline to form the final strategic piece in his bid to build the world's first global aviation alliance. BA has taken equity stakes in four carriers worldwide, but is still without a partner on the important North Pacific routes and has little in the way of intra-Asia services in its grouping. ''I would hope that in the due course of time we will be able to enter into a partnership agreement with a good strong airline in the Asia region which will provide our global alliance with North Pacific routes as well as a substantial network of intra-Asia routes,'' said Sir Colin yesterday on a visit to Hong Kong. BA has stakes in Qantas of Australia, Deutsche BA of Germany, TAT European Airlines of France and USAir of the United States. BA and Qantas operate some services to Asia, but none has a particularly strong presence in the region, which has the world's greatest growth in the number of passengers. Qantas serves the south Pacific, but not the north. Sir Colin said no formal negotiations had taken place with any Asian airlines, although the idea of joining the grouping had been informally suggested to some. Sir Colin yesterday seemed unperturbed at the prospect of Virgin Atlantic Airways launching flights between London and Hong Kong, breaking the duopoly on direct flights enjoyed by BA and Cathay Pacific Airways. Virgin, BA's fierce business rival, has pledged to heavily undercut the pair to steal market share on this busy and lucrative route. It has proved the success of this tactic when starting services elsewhere. But Sir Colin yesterday said: ''We have seen Virgin come on to a select number of the densely travelled routes that we fly and it hasn't really affected us at all. ''We have continued to do extremely well on those routes and have maintained very good load factors,'' he said. ''We have, in most cases, maintained our relative proportion of the market share, recognising that if somebody new comes in they have to take part of the 100 per cent pie. ''But relative to the other carriers flying that route I think in every case we have either maintained our share or increased it.''