THE pro-UK Better Together campaign is to ramp up its advertising this week as the independence referendum passes a key legal milestone.

The group yesterday said it would distribute 2.3 million leaflets across Scotland, take out full-page adverts in national and local newspapers, and send 300,000 letters to female swing voters.

The acceleration coincides with the start of the final 16-week "regulated period" on May 30, when all campaigners become subject to strict rules on spending, donations and behaviour.

The regulated period sees spending caps of £1.5 million imposed on both Better Together and Yes Scotland as the designated lead campaign groups.

Spending by the political parties is set in proportion to their share of the vote in the 2011 Holyrood election: the SNP limited to £1.34m, Labour £831,000, the Conservatives £399,000, and the Liberal Democrats £204,000. The Scottish Greens, Scottish Socialists and "permitted participant" groups such as Women for Independence, National Collective and No Borders can spend up to £150,000.

Better Together also said former Sunday Herald business editor Ken Symon had been hired to liaise with employers worried about a Yes vote, while Highlands journalist Jim Innes joins the press operation.

Better Together campaign director Blair McDougall said: "When nationalists won't tell us what would replace the pound, how pensions would be paid and what would happen to the money available for our schools and hospitals, it's no surprise all recent polls show Scots rejecting Alex Salmond's obsession with separation."

Yes Scotland said it is concentrating on the next big date: 100 days to go on June 10.