The new Deregulation Act 2015 finally lays this ghost to rest. I must point out that we at Visum were of the opinion that the ruling by Lord Justice Lloyd did NOT mean that you had to re-protect a deposit every time a tenancy became periodic, and that his ruling only applied to tenancies created before 6th April 2007 whereby there had been no requirement to protect a deposit in the first place. However we held a minority view it seems, and the Internet was (as usual) full of different opinions.
Thankfully the Deregulation Act fixes the issue and you now do not have to reprotect deposits when a tenancy becomes periodic. However if you do still have a tenancy that was created before 6th April 2007 and where a deposit was taken and has not as yet been protected, you have until June 23rd 2015 to get it protected. It's worth pointing out that if you have a tenancy that became periodic before 6th April 2007 you do NOT have to protect the deposit, but you won't be able to evict with a Section 21 if you don't, so it's still well worth protecting the deposit.