Trimmer entered six Formula One World Championship Grands Prix with uncompetitive teams, firstly Maki for four races in 1975 and 1976, resulting in four failures to qualify. He then entered the 1977 British Grand Prix (failed to pre-qualify) and the 1978 British Grand Prix (failed to qualify), with the Melchester Racing Team, driving a Surtees TS19 and a McLaren M23 respectively. However, also driving the Melchester McLaren, he finished a superb third in the rain-soaked 1978 BRDC International Trophy non-Championship race at Silverstone, coming home ahead of many of the greats of Formula One. That year he won the British Aurora F1 Championship.