I am mildly suprised that having gone through a complete course you are unaware of just how tiny the UK banner/crop market is. Basically there is NO crop spraying and banner towing is at best a very small half dozen aircraft utilised in the summer by the same old faces.
You should be looking more towards instructional work (not easy) or safety pilot work (not paid and its all about contacts). Some airlines ARE actually taking low time guys - mine for one - although they don't shout about it much so do keep plugging away.
To be honest the miserable few hours and no money that you are likely to get from the above is not worth it IF you can go and earn a decent crust elsewhere outside of aviation. If you save some cash and spend it on some decent twin sim time in 6 months - perhaps with a small syndicate - you would be better off.
Cheers,
WWW