Castle Cement delivery drivers are set to escalate their industrial action after a one-day strike last Thursday over derecognition of the transport union TGWU.All 220 drivers at Castle's plants stopped work after voting 96 per cent for strike action in a ballot.Terry Jane, Castle's group personnel manager, claimed the effects of Thursday's action had been 'minimal'.He said: 'We achieved pretty near a 90 per cent delivery pattern because we had contingency plans in place.'There was very little effect on our customers on Thursday.'But TGWU national secretary Len McCluskey said he was 'extremely pleased' with the action.'For the company to say they had 90 per cent is ludicrous. We're more than aware that isn't the case.'He claimed the contingency plans, which included stockpiling supplies and bringing in contract drivers, had cost Castle 'considerable amounts of money' and that supplies had been wasted because Castle misjudged the timing of the strike.Mr McCluskey pledged: 'There will be a series of strikes and we will escalate the action as far as we see fit.'He would not comment on the timing of any future action because the union aims to maximise disruption with last-minute strike calls.But he added that Castle's process and craft workers were 'looking at this situation with more than a little interest'.The dispute has been rumbling for months after Castle tried to impose new contracts based on individual performance which derecognised the union.So far the company has refused to meet the TGWU at a national level.Mr Jayne said no national talks were planned and Castle was determined to press ahead with its proposals to increase the efficiency of its transportation service.