If you wish to continue using spreadsheets to prepare accounts then you can. The Ftax CT600 includes iXBRL Accounts tagging to convert your accounts data into iXBRL. Note: this is only included on the post 31st March 2015 ‘V3’ CT600 form, and is NOT included with the older ‘V2’ CT600.
Alternatively, you can use VT Final Accounts which will make it very easy for you to map the final accounting figures to the XBRL data standard to produce the iXBRL files.