The first victim of the changeable weather conditions was the GA Janspeed Alfa Romeo of Gavin Pyper who went off on the approach to Tower Bend on Lap 12. The Safety Car was sent out whilst the Alfa Romeo was cleared and Muller lost the 6.7 second advantage he had built throughout the race.
The fastest pit stop of the day was by the Peugeot team who changed the tyres on Dan Eaves' car in an impressive 6.9 seconds.
On Lap 19 the Peugeot of Steve Soper and the Team Egg Sport Astra of Phil Bennet were side by side throughout much of the lap. It was inevitable that contact would be made at some point and it was Bennett that looked to come off best as Soper was forced wide off the track. Soper came back though and ran into the back of Bennett's car, knocking both cars off the circuit. The damage to the Peugeot meant he would later retire from the race on Lap 23. Bennett also retired but from a spin at Tower bend. The Safety Car was deployed for a second time.
The deployment of the Safety car created problems for Lemmer on the restart and Jim Edwards Junior took advantage to nudge past Lemmer on Lap 24. The rear wheel tyres were clearly beginning to wear at this late stage of the race and an off from the Tech-Speed Peugeot of Paul O'Neill, also at Tower bend, pushed the Safety Car out for a third occasion.
Muller made the most of the restart to take a comfortable lead and the chequered flag. Team mate Plato held on to second ahead of a disappointed James Thompson in third.
Muller said: ''I would have preferred it if the race was in dry conditions as I knew I would not be quick enough. I started with low tyre pressure as the track wasn't really wet, but then it got worse so I decided to come in and asked for normal pressure tyres in the pit stop, but I couldn't stop when I wanted to as James Thompson came in so I decided to stay out for one more lap and that worked. When I did stop, my fronts were better than the previous set. The re-starts became more difficult as you have to concentrate more and more.''
Jim Edwards Junior took his first win of the season and added his name to an ever expanding list of 2001 BTC Production winners. GR Motorsport's Mat Jackson had a trouble free race to come home in second with his team-mate Gareth Howell clinching third in the Ford Focus.
Edwards said: ''In these conditions, it is a case of consistency, concentration and finesse and to be honest, the emotions that went through my mind on the last lap were amazing! Mat (Jackson) gave me a right old belt at the hairpin which put me completely sideways and put me into the wall. I couldn't believe I bounced off and back onto the track to regain first place. I think someone was looking down on me and it was the best race of my life!''
The win for Yvan Mulller means he now leads the BTC Touring Championship with 235 point over team-mate Plato who is three points behind (232). In the Production class James Kaye leads Simon Harrison by four points with a total of 155 points as opposed to Harrison's 151.
TOCA Officials made a post race decision to ban Phil Bennett from Round 19 of the Championship following reckless driving from the Team Egg Sport driver in Round 18.