Robert the Bruce's invasion of English occupied Ireland in 1315 could have created a Celtic empire to challenge English dominance of the British Isles. This two part series explores one of history's most fascinating 'what ifs'.

In the first episode, Robert the Bruce's victory over the English at Bannockburn in 1314 did not put an end to Scotland's fight for independence. King Robert knew that his crown was not secure so he decided to open a 'second front' against the English and invade English occupied Ireland.

Robert and his brother Edward hatched an audacious plan - with the help of allies in Ulster they would unite the Scots and Irish in a powerful Celtic alliance against the English threat. In May 1315 a Scottish army landed in Ulster. The Bruce invasion looked like a great success.

The Gaelic Irish, disgruntled after 150 years of English oppression, would welcome the Scots with open arms. And at first, all went well - Edward was recognised as High King of Ireland by several leading Ulster lords. A formidable leader, he won a number of significant battles and captured English strongholds.

Was this the fulfilment of the widely believed prophecies of Merlin about a new King Arthur uniting the Celts?