The Prime Minister launched into a brief argument for Scotland remaining as part of the UK after the Scottish referendum in 2014.
He said he believes the case for union can win the "arguments of the heart" as well as the "arguments of the head".
He said he is proud of what the UK has achieved together, such "defeating fascism" and the NHS and BBC.
But he also drew attention to the more than 12,000 people in Scotland employed by the defence industries, which he said were backed by the whole of the UK.
More top news
Cricket stars, celebrities and fans have joined a social media campaign paying tribute to Phil Hughes by leaving their cricket bats out.
Eight out of 10 asthma sufferers are not getting enough clinical care, a leading health charity has found.
Phillip Schofield has revealed that an eccentric fan who wanted to marry him arranged a wedding - leaving him with the bill.