You probably have a driver or two missing that are only available from the Sony Vaio support website appropriate for your country.
Go here for the UK website:
http://www.sony.co.uk/support/en/hub/VAIO
If you need to change the country, click the UK flag at top left of page.
Looking at the Windows 7 driver section for that model here: http://www.sony.co.uk/support/en/product/VGN-BX61XN/updates, there are no Windows 7 drivers listed. There's only a "Vaio Update Utility". Download and install that and see if it updates your Vaio with the software required for the keyboard to function properly.