Ah ha.. it has surfaced:
|------------------------------------------------------------------------------------------|
| WinMTR statistics |
| Host - % | Sent | Recv | Best | Avrg | Wrst | Last |
|------------------------------------------------|------|------|------|------|------|------|
| 192.168.1.1 - 0 | 124 | 124 | 0 | 0 | 15 | 0 |
| 192.168.0.1 - 0 | 124 | 124 | 0 | 0 | 15 | 0 |
| dr10.ennby.ov.easynet.net - 0 | 124 | 124 | 31 | 32 | 47 | 31 |
| 5acf0026.bb.sky.com - 3 | 124 | 121 | 31 | 45 | 62 | 46 |
| be2.er10.txlon.ov.easynet.net - 3 | 124 | 121 | 31 | 46 | 63 | 46 |
| ae0-461.rt0.sov.uk.goscomb.net - 1 | 124 | 123 | 31 | 48 | 125 | 46 |
| ae0-1624.rt2.the.uk.goscomb.net - 4 | 124 | 120 | 46 | 51 | 187 | 46 |
| tele-north.killercreation.co.uk - 3 | 124 | 121 | 46 | 51 | 203 | 46 |
| Service.alpha-networks.co.uk - 3 | 124 | 121 | 31 | 46 | 62 | 46 |
|________________________________________________|______|______|______|______|______|______|
WinMTR - 0.8. Copyleft @2000-2002 Vasile Laurentiu Stanimir (
stanimir@cr.nivis.com )

No sign of any application using loads of bandwidth or anything. I'm going to not reset the router, and see if it goes away of it's own accord.