The Guardian, which has always stayed out of previous price wars, was widely expected to follow suit.
The Guardian is now the same price as The Independent and the Telegraph, which were the first to raise their cover price, followed by The Times, which at 45p remains the cheapest paper in the broadsheet market.
Carolyn McCall, managing director of Guardian Newspapers, said: "At 55p, The Guardian offers fantastic value for money to our readers. This price increase will allow us to invest yet further in the most innovative newspaper in the country. At long last, the market is recognising the extraordinary value of newspapers and this is good news for the industry as a whole."
The Times has followed rivals The Independent and The Daily Telegraph by raising the cover price of its Monday-to-Friday editions to 45p, suggesting the broadsheet price wars might be over for now.
The price rises bring an end an almost decade-long price war initiated by Rupert Murdoch's UK newspaper business News International in 1993 when The Times dropped its price to 30p and, at one stage, 10p on Mondays in an attempt to boost sales.
Despite the Times's price cut in 1993, the Telegraph has retained its lead in the weekday broadsheet market, with an ABC circulation of 1,002,739. The Times, which put its price up to 40p in June last year, had hoped to overtake the Telegraph and, even though it failed to hit that target, its sales have almost doubled to 677,524.
The Independent's circulation is languishing at 224,876, behind The Guardian, which has an ABC of 387,239.
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