The needs of your staff and your business model are the main drivers on this decision.
Your first hire may be key initially and a business could be built around that person, which can dictate the location. Using a managed office service, or a virtual office, could be useful until such time as the business becomes established.
When moving from a one person operation to a team environment then the travelling needs of the team as whole, and the location of your customers becomes important.
When it’s time for the company to expand you will want to take advantage of the available skills and synergy within your industry sector. The UK has a range of clusters that can provide these in world-recognised locations. For example, hi-tech in the Thames Valley; financial services in the City of London; pharma in Cambridge; green energy in the south-west; and low carbon in north-east England.