Alex Salmond's SNP outspent Labour for the first time in May's Holyrood elections by more than £280,000 as the Nationalists almost trebled their campaign spending to a record £1.4m, not far short of the statutory limit.

Figures released by the Electoral Commission yesterday revealed that the four main parties spent a total of £3.4m this year, more than double the £1.6m they spent in 2003.

Backed by wealthy donors such as transport tycoon Brian Souter, who, according to the commission's register, gave the Nationalists £625,000 in the first part of the year, the SNP spent £1,383,462 in May's poll, up from £473,107 four years ago, which represented a rise of 192.4%.

Labour spent £1,102,866, up from £726,702 in 2003, an increase of 51.8%. The Conservatives spent £601,983, up from £323,279, a rise of 86.2% while the Liberal Democrats spent £303,740, up from £130,360, a rise of 133%.

By law, the parties have to say what they spent their money on. The records for the May poll showed that by far the largest expenditure went on mailshots to voters and advertising, £939,444 and £977,836 respectively. They also spent a significant amount on market research and canvassing as well as overheads and general administration, £366,161 and £381,027 respectively.

Spending was placed into nine categories with the SNP spending most on political broadcasts, advertising, and mailshots, while Labour spent most on transport and rallies. The Tories, meantime, spent by far the most on general administration.

MP Angus Robertson, SNP business convener and 2007 campaign manager, said: "The SNP ran an overwhelmingly positive campaign that caught the attention and imagination of voters across Scotland with a strong vision for the future of our country.

"As the latest opinion polls show, that popularity continues to grow as the SNP Government delivers on our manifesto and moves Scotland forward amidst a new tide of optimism across the country."

However, a Scottish Labour spokesman said last night: "The SNP may have spent thousands of pounds more than any other party but the fact is that they were spending it on advertising election promises they knew they ... were never going to deliver."

Andy O'Neill, head of the Electoral Commission's office in Scotland, said: "The information released today on campaign spending is an important part of ensuring full transparency in the democratic process in Scotland.

"These figures allow the voting public to see not just how much money parties spent on campaigning but also what they spent it on. Together with the figures from the 2003 Scottish Parliamentary election published by the commission, the electorate have - for the first time - the opportunity to see how spending at these elections has changed over time."

He added: "The figures show that spending among the large parties has increased dramatically in comparison to 2003 and that Scottish Labour and Scottish National Party expenditure is now close to the statutory limit."

The 2000 Political Parties, Elections and Referendums Act imposes spending limits on parties contesting the Scottish Parliamentary elections.

These are £12,000 per constituency and £80,000 for each region contested by the party.

For a party standing candidates in all constituencies and regions - as the top four all did - there is an overall spending limit of £1,516,000.

What it cost the main parties
SNP
Political broadcasts £90,726
Advertising £494,642
Mailshots £323,580
Manifesto £56,999
Market research & canvassing £178,705
Media £45,041
Transport £52,239
Rallies £64,652
General administration £76,146

Labour
Political broadcasts £59,685
Advertising £337,609
Mailshots £270,020
Manifesto £17,525
Market research & canvassing £107,477
Media £29,710
Transport £72,366
Rallies £89,685
General administration £118,789

Conservatives
Political broadcasts £29,338
Advertising £119,419
mailshots £247,521
Manifesto £9134
Market research & canvassing £15,353
Media £17,957
Transport £2243
Rallies £270
General administration £160,747

Liberal Democrats
Political broadcasts £15,381
Advertising £26,166
Mailshots £98,323
Manifesto £6905
Market research & canvassing £64,626
Media £29,481
Transport £29,635
Rallies £1710
General administration £25,345