Bemused spectators arriving at the ground wanted to know if there had been an overnight X Files-type visitation in SE19 - but the truth was less outlandish, if equally advanced technologically.

The England and Wales Cricket Board explained that the markings are being used experimentally as targets for the television cameras to create 'virtual advertising' - images electronically superimposed on to live action.

The advertisement appears to viewers to be part of the actual event but is not visible to players or spectators.

Terry Blake, the ECB's marketing director, said: ``We want to see if this can be a feasible way of generating extra revenue. But we must make sure that such advertising is not obtrusive for the viewer or the broadcaster.''

This could open the way for tobacco advertising to associate itself again with cricket here, albeit by the back door, with the advertising targeted at audiences in countries where it is still permitted.

If successful, the experiment - which has been approved by the ICC - would be converted into advertising deals packaged with overseas markets in mind. The ECB stressed that the idea was very much in the evaluation stage.