Wanted: Any freelance IT guys willing to offer your services..?

I think you may be right.

I have just spoken with them and apparently in Dec and Jan our usage was up near 50 whatever bytes per month, we only used 10-15 whatever bytes per month previous to this.

They are having a look to see what may have caused this.

I'm always right. Just that it might be days/months/years later ;)

I'd check all the machines on your network (inc. any laptops on your wifi) for latest antivirus definitions and scan 'em. If you have a packet sniffer/bandwidth monitor you could analyse heavy traffic and narrow it down to a single connection. If not, you migth have to go around and turn PCs on/off until you find the culprit.

Also, try asking users to stop doing any network instensive stuff like streaming for a while to see if it makes a diff. Depends on your work environment as to what you can get away with doing.