Hmm, I'd suggest closer to £50 than £100 - it needs new cables, bar tape and brake pads for sure and possibly new chain and freewheel too depending on the condition. I'd also be concerned about the seat post and stem being seized as well as the headset and bottom bracket condition. Chances are it needs a few hours of labour putting into it - if you do this yourself it's free but you'd expect to drop the price to compensate for this.
If you want to obtain the most value for the bike then parting it out is likely to be your best option - particularly with that Cinelli stem.