This belt kit fits the VTC 5000 series (not 5300, 5400) but it also fits the front loading models and that's why you have 4 belts. The first belt is the reel/idler belt. For the loading belt, I would try the second and the third one. A new idler assembly can be purchased here:
http://studiosoundelectronics.com/mbk-49.htm
Keep in mind that this website is from the USA but I'm sure you can find these in the UK too.
Fivos