Have you tried 'SLIP' No More Webs! It's on Amazon and has done the trick for me. Here's the info
Prevents Spiders Spinning their Webs over CCTV Camera Lenses. Tried and Tested.
• Developed in Collaboration with the UK's Leading Arachnologists.
• Very Long Lasting and Durable.
• Does Not Wash Off like most Sprays and is Non Drip.
• Very Effective as a Barrier on Ant Farms.
http://www.amazon.co.uk/gp/product/B00O6E71IA/ref=cm_cr_dpvoterdr?ie=UTF8&keywords=no%20more%20webs%20cctv&qid=1433364301&sr=8-1&thanksvoting=cr-vote-R2RUQE5L1FNWG4#R2RUQE5L1FNWG4.2115.Helpful.Reviews