ALLEGATIONS of assault by police officers have soared by 24 per cent. Figures released by the Police Complaints and Internal Investigations Branch yesterday showed 540 assault complaints were lodged between January and March. Assaults formed more than half of all complaints against police. The number of assaults so far this year is up 105 on the same period last year and up 31 on the last quarter of 1992, which is a six per cent rise, in keeping with general trends for several years. Allegations of fabrication of evidence, neglect of duty, unnecessary use of authority, and misconduct were also up, while claims of offensive language and threats receded. Acting chief staff officer at the investigations branch, Chief Superintendent Ross Williams, said individual complaints were being scrutinised to find out the reason for the rise. Front-line police expressed concern that morale problems had led to frustration and aggressiveness but officially the force was quick to play down the figures. Mr Williams described them as a ''very disturbing statistic'' but was adamant that it did not mean that police were more readily stepping out of line. ''I do not accept there is an increase in actual assaults. What we have is an increase in allegations of assault,'' he said. ''The reason for the increase is not easy to determine, but we will get to the bottom of it.'' Officers said, however, that the force was now bearing the brunt of morale problems stretching over 18 months. ''Unhappiness leads to bad discipline and one of the ways this always manifests itself is shoddy police work, including [officers] taking their frustrations out on the public,'' one senior officer said. Mr Williams said 80 per cent of all assault complaints related to crime reports and investigations and were ''tactical'' allegations to back up pending court cases. A similar number of assault allegations were withdrawn or not pursuable. The reasons why so many complaints were withdrawn or considered not pursuable were investigated last month by the official complaints watchdog, the Police Complaints Committee (PCC). Mr Williams said that police were not encouraging people to withdraw complaints. The force's own research suggested many people did so because they could not be bothered continuing. He said he wanted to maintain the thoroughness of police internal investigations and would only seek to simplify procedures if asked by the PCC. In total, 906 complaints were lodged in the latest quarter, up 19 per cent on the same period last year and one per cent on the last quarter of 1992. ''It seems that overall the increase in complaints may have now almost levelled off, despite the fact that CAPO [the Complaints Against Police Office] has been very much in the public eye,'' Mr Williams said. ''Nevertheless, much is being done within the force in an attempt to curb complaints and provide a better service to the public.'' Mr Williams said he hoped a new complaint prevention video being shown to front-line officers throughout the territory would stop officers putting themselves in situations which forced complaints. The video is backed by the force's own new Complaints Prevention Committee. The group, made up of 15 front-line and senior officers, met for the third time last week and decided to work on areas where complaints could be actively avoided - chiefly face-to-face dealings with the public. A review of police conduct at roadblocks and stop-and-searches was under review by the committee. Mr Williams said the techniques themselves were not under examination but the way individual police dealt with the public. ''It's a matter of reducing complaints through re-education,'' he said. ''We're keen to ensure officers know what constitutes reasonable suspicion and the correct manner for dealing with the public in these situations,'' he said.