Greater changes took place when the Uniform Penny Post was introduced on 10 January 1840, whereby a single rate for delivery anywhere in Great Britain and Ireland was pre-paid by the sender. A few months later, to certify that postage had been paid on a letter, the sender could affix the first adhesive postage stamp, the Penny Black, which was available for use from 6 May the same year. Other innovations were the introduction of pre-paid William Mulready designed postal stationery letter sheets and envelopes.