The kind of solar panels being sold for installations in the UK have been designed to work best in daylight conditions and not necessarily direct sunlight. As a result, anywhere in the UK is suitable for solar panel installations, especially for domestic use. It is the larger scale commercial solar farms that will notice the benefits of choosing an optimum location for daylight intensity.
The government have defined a set of standards for the solar panel installation industry in the UK. These are known as SAP (Standard Assessment Procedure) and take into account the angle and orientation of your roof, the location of your property and a number of other factors to calculate the energy generation performance of your home.
The map below shows how daylight intensity varies across the United Kingdom, with the South West (coloured in red) having the best locations for solar power generation.