The government updated its guidance for employers about the Coronavirus Job Retention Scheme on 4 April 2020.  This included confirmation that employees could be furloughed "multiple times", each separate instance being for a minimum of 3 weeks.

Previous guidance for employees published on 26 March had indicated that they might be furloughed "more than once" and “one period can follow straight after an existing furlough period”, which suggested that there may also be a gap between periods of furlough.

As well as checking for updates to the employer guidance, it is worth checking the updates to employee guidance.

https://www.gov.uk/guidance/check-if-you-could-be-covered-by-the-coronavirus-job-retention-scheme