Its often worth having a Tax Group even if you don’t have Group Accounts ie you have multiple businesses under common control but that are not directly owned subsidiaries. The reason for this is to offset profits and losses to reduce the total tax payment.
Generally this means completing a special extra return, the CT600C, unfortunately, this form is not available from HMRC to file on line.
There is a solution regulation 6 SI199/2975 (CTM97690) allows you to write to HMRC and explain which companies make up the group and ask for a simplified arrangement – meaning HMRC will automatically net off the returns with out the need for CT600C returns.
By doing this you can file the CT600’s on line for free with HMRC.