As you can see there is a layer of dirt and insects like a carpet in front so out came the toothbrush and the hoover together with some solvent spray and an air blaster, the results were quite a lot better although its difficult to see in the pics.
Finally whilst re-assembling i was trying to think of where i could install a filter and what i could use. My wife came to the rescue as usual and said "you could use tights"
One pop sock later
Hopefully this will keep all the insects and large bits of dirt out and can be replaced easily.
Sorry if this has been detailed before but i thought i`d show you what i was up to.
Clive
But it's a great idea. Might buy myself some tights - do you recommend any particular colour? 
may let a bit too much through 
