You will no doubt be aware that the new flexible furlough scheme will be starting on 1st July 2020. I have summarised the main changes in https://cheringtonhr.com/news/592
and since then it has been announced that returning reservists can also be included along with those who have been away on maternity and other forms of statutory family leave.
However, the Treasury Directive - the official instruction to HMRC to process claims under the variation to the scheme has been published on the Government website at https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/895778/Further_Treasury_Direction_made_on_25_June_2020_under_Sections_71_and_76_of_the_Coronavirus_Act_2020.pdf
This is the legal document that modifies the original directive when the scheme was set up back in March 2020. If there is a conflict between the guidance originally published, this one takes precedence. It is fiendishly complicated and stretches to 34 pages long. So my advice is to talk to your payroll provider to find out how they want the information they need to process any claims you wish to make going forwards. And if you don't have a specialist payroll provider, but having read this think you need one, (but don't know who to ask) get in touch and I can give you some recommendations.
If you are going to put staff on flexible furlough working arrangements do not forget to get agreement from the affected employees, and put in place new furlough agreements to allow shorter periods of furlough interspersed with periods of working. If you need assistance with this, please ask.