Gillian,
You were legally obliged to register for tax from the point at which you became 'tax resident' here. i.e. 183 days in a calendar year present in Cyprus. Many people labour under the misconception that it is optional to register for tax purposes. Whether or not the authorities will penalise you for not registering, I can't say. I suggest you head down to the tax office with all of your paperwork. you will need to complete HMRC form DT/Individual available from http://www.hmrc.gov.uk/cnr/dtindividual.pdf and take it with you to the Cyprus tax office. They will send it to the UK.
All the best