Subsidence is when the soil supporting the house sinks. It is caused by certain soils, vegetations, leaking drains, mines, heave (upward movement of the ground) and landslip (downward movement of the ground). If your house is subsidence-prone, your premiums will be higher because the risk is higher. But you could be able to insure if repair work is done and you mimize the risks:
If diagonal cracks wider than the edge of a 10p piece appear on your wall, contact your insurer.
Planting trees but consider the variety, the soil type and stay away from shallow-rooted trees. Plant them at a distance of their expected mature height.
Don’t remove trees especially if they’re planted on clay soil, because the soil could swell.
Prune trees and shrubs and clear gutters, check for pipe leaks.
Have a full structural survey of your house to identify potential problems.
Sources:
http://www.thisismoney.co.uk/help-and-advice/advice-banks/article.html?in_advicepage_id=101&in_article_id=394211&in_page_id=90
http://www.coverdirect.co.uk/home-insurance/subsidence.aspx