LLP Tax Return

Got an LLP client, originally 2 partners but one left and has not been replaced. On the basis that an LLP is a separate legal entity I completed Partnership Tax Returns for the years in which there was only one partner. These have now been returned by HMRC as business is effectively a sole trader. I had been under the impression that because it was an LLP a Partnership Return had to be submitted regardless of the number of partners. As I understand it there is nothing to stop an LLP having only one member - the major effect is that after a period it loses it's limited liability. All comments gratefully received.