Gutters should be cleaned ideally twice a year. once in the autumn after the leaves have dropped, and in the spring after the birds have finished pecking the moss off the roof to help build their nests.
If cleaned on a regular basis you could avoid the possibility of having to make an emergency call or suffering damage from water pouring down the side of the house from blocked gutters.
Blocked gutters can also become damaged from the weight of the water, causing them to sag or come away from their fixings altogether.
Kingfisher Windows and Gutters, 5 Pine Walk, Northchurch, Hertfordshire. HP4 3YZ