When booking flights you will find that booking early gives you the best prices. Most flight details are available on-line 8 months before departure, therefore, I would recommend you look to book your scheduled flights within that time scale. When looking at Charter Holiday flights the best deals can be found by leaving it to within 6 weeks before your desired departure date, unless you are looking to travel at peak times, such as school holidays or bank holidays, when availability could be in short supply.
All main airports, stated above, have direct train services and bus/coach services and access to car-hire companies.
For internal domestic flights see the Travelling Around Britain page.
Main Ferry Terminals: Harwich, Dover, Portsmouth, Plymouth and Hull.
Main UK Eurostar stations: Ashford, St. Pancras
For details see: Eurostar
The UK Foreign and Commonwealth Office is the government department responsible for promoting British interests overseas: Travel & living abroad