You may be able to get support or grants for other improvements such as replacing single glazed windows, upgrading old gas boilers to a condensing boiler, or installing insulation. There are various sources, and things change all the time.
Try the Energy Saving Trust for up to date information.
Support in Hull
Hull Warm Zone offer free, independent and impartial advice to householders in Hull, and provide access to grants, advice and support which make homes warmer and cheaper to heat.