Almost everything you need to know is on this site Steve:

http://www.energysavingtrust.org.uk/...n/Find-a-grant

There are different (subsidised) schemes in different parts of the country, so as always, contact SEVERAL different installers, the details of whom can accessed from the above site.

I leave you to use your own judgment as to whether it will be financially worthwhile for you Steve, but bear in mind that external insulation will physically alter the appearance of your house, as you're adding around 4" or more to the external wall dimensions. On a semi or terrace, this will mean that the walls will be 'proud' of your neighbour's, so ideally, best installed together.

The work will probably take about a week.