It depends where you are going to live and how you are going to pay for your new accommodation. If you are moving within the UK and intend to buy another house you run into the problem that you will find it hard to get a second mortgage. If you rent out the house in Kent you will probably have to change the mortgage basis on it to a mortgage that allows for letting - normal residential mortgages exclude that entirely - which would allow you to take out a residential mortgage.
It depends how much equity you have in the house. If most of the value of the house is mortgaged then you'll (1) find it hard to re mortgage on a commercial mortgage (2) may find it hard to cover the costs by letting and (3) are very sensitive to house prices falling.
Also bear in mind that for the past three months in a row, house prices in the UK have mostly either stagnated or fallen... so you cannot guarantee any increase in value of the house in Kent.
What I'm saying is ... there is no crystal ball that will tell you what's financially the best thing to do. Talk to estate agents, find out how much the house would sell for / how much it would rent for. Talk to your mortgage lender and find out if they will let you rent it out. Talk to other mortgage lenders and find out how much a commercial mortgage would cost. Do the sums, find out if renting the house would cover the costs, in which case you can gamble on the housing market continuing to rise. Don't rely on house prices continuing to rise as they have done before. Certainly where I live due to the number of new houses being built and other economic issues house prices have fallen appreciably over the past few months and may well continue to fall as more and more new houses come on the market.