If you know, or even suspect, that your property has undergone subsidence or has been underpinned, it is much wiser to act than ignore it. Surveyors are becoming increasingly worried about cracks, bulges and window/door joinery distortions, commonly referring such problems to a specialist. Faced with a choice, they would rather delay your sale than risk a negligence claim. This can delay the sale at its most critical stage, usually for months, sometimes years.
The good news is that there are many conditions that give subsidence-like symptoms, and a knowledgeable defects specialist will discover whether the true cause is something else – such as, shrinkage/expansion (thermal or materials-based), lintel failure, weathering effects, etc. Some subsidence conditions are very localised – for example, that caused by a water mains or drains leak. Others are more general – perhaps due to clay soil expansion/contraction, or a rise/fall in water table.
If you deal with it early, you will have all the right pieces of paper in place when you sell. Reports on drains, soils investigation, specification, a completion certificate, etc, will help satisfy your purchaser’s surveyor, mortgage lenders and (above all) insurers, who should continue to insure the property for the new owner.
Often your buildings insurers will pay for the cost of underpinning, drains repairs and making good, and the professional fees involved, less an “excess” – typically £1,000. This may sound a lot, but it can be so much cheaper than a price-reduction, abortive legal costs, and losing the chance to move to your next property. But do allow many months for this process!