If you have a few thousand pounds spare then it's better to invest it on solar photovoltaic panels than leaving it in the bank. The Feed In Tariff pays you 38p per kWh (or something like that). In addition, if you are out, you can export that electricity to the grid and your utility provider pays you an extra 3p per kWh (so that's 41p per unit). If you are in, however, not only do you get your basic 38p per kWh, you also save the 15p per kWh you would have paid your utility provider for the electricity you didn't use (53p per unit). The panels should pay for themselves between 10 and 15 years. PV panels last a long time, 25 years or more, because they have no moving parts. Cables may corrode over time and the panels may lose efficiency, but they'll still last 25 years. You may have to replace your inverter after about 10 years. A kWh is a unit of electricity BTW.
One thing to bear in mind is that the tariff you get will decrease every year you leave it. This is because it is anticipated that the costs of installing the PV panels will reduce once economies of scale start kicking in. The high initial price to help kick-start the PV industry.
The only other thing I would worry about is whether future governments would honour the agreement. It's actually the electricity companies who are forced by the government to pay you, funded ultimately by their other customers. I expect future governments will honour the scheme. I suspect what a future government might do is restrict the scheme for new takers, but honour the payments to those who are already signed up. There was a similar sort scheme in Spain. The Spanish government would like to stop making the payments because they are in deep economic trouble, but they can't because they'd be sued. I suspect it would be the same here.
Without the Feed In Tariff, solar photovoltaic panels would never pay for themselves. They also have to be installed by an accredited installer and connected to the grid to qualify for the Feed In Tariff.