Plane with three of four contrails?

[flight cat]

Hi all,
I've been reading these forums for about 3 years now, thought I'd sign up because I saw something odd (or maybe not!) in the sky on Saturday...

I was in the Gravesend area of the UK, and after lunch in the pub, I saw a plane fly directly overhead, possibly in a vaguely south western direction, and it looked to be pretty close to cruising altitude. The wierd thing was that the plane only had 3 vapour trails behind it, 2 close together on one wing, then a big gap, and a single trail on the other. I guess that means one of the engines was shut down?

I couldn't see anything on the rumours forum, does anyone have any idea what plane it was or what was wrong?

thanks
fc