EU referendum: Europe's media see Johnson as boost for Brexit

"A new Battle of Britain" says Italian newspaper La Stampa

Many European commentators have reacted to London Mayor Boris Johnson's decision to back Britain leaving the European Union, seeing his intervention as a problem for Prime Minister David Cameron.

But in Central European media, the main focus is on the impact of the referendum on benefits for migrant workers in Britain.

• Follow the latest updates with the BBC's EU Referendum Live

• EU leaders and the struggle with UK's 'special status'

• The UK's EU vote: All you need to know

• Remain v Leave: Where Conservatives stand

• Paper review: Johnson dominates front pages

Germany's n-tv news channel says Boris Johnson's intervention is a "serious setback" for the prime minister, despite the mayor's pledge not to go up against Mr Cameron in any television debates.

Olivier Bories dubs Mr Johnson the "man of the moment for Brexit" in French Catholic daily La Croix, saying that the London mayor is, "despite his constantly dishevelled blonde mop, a politician to be taken very seriously".

Like other commentators, Mr Bories highlights Mr Johnson's high media profile, but also recalls his record of gaffes at home and abroad.

Nonetheless, he does not doubt that his "carefully timed" announcement positions him as a possible successor to Mr Cameron in the event of a vote for Brexit.

"Battle of Britain"

Philippe Bernard, London correspondent of France's left-of-centre Le Monde, agrees that Boris Johnson's "defiance" of David Cameron gives a "potentially decisive impetus" to the Brexit campaign and could see him oust the prime minister.

A Russian pro-Kremlin TV channel sums up Boris Johnson's move as a "stab in the back"

He rates Mr Johnson's role as important, but also considers his "capricious personality and unpredictable political opportunism irritating to the British public" and perhaps a "threat" to the Conservative Party and the country itself.

Alessandra Rizzo in Italy's liberal La Stampa is not alone in rehearsing the personal rivalry between the prime minister and mayor, whom she dubs "perhaps the most popular politician in the country", but goes further than most in ranging them against one another in a "new Battle of Britain".

"Expect four months of intense, even heavy skirmishes" between the two Conservatives ahead of the June vote, she concludes.

Russia's pro-Kremlin NTV channel uses an even more heated analogy, dubbing Boris Johnson's move "a stab in the back".

"Lose both ways"

In Hungary, the Nepszabadsag daily is gloomy about the impact of the UK referendum on developments at home. If Mr Cameron prevails, it concludes, "Hungarians working in Britain can say goodbye to part of their welfare benefits... but they lose even more if supporters of quitting win".

Tomasz Bielecki, Brussels correspondent of Poland's liberal Gazeta Wyborcza, agrees that migrant workers like the Poles "will pay most for Mr Cameron's compromise", but concludes that "if it keeps Britain in the EU, it's a price worth paying".

A British exit would weaken the European Union, especially in its dealings with Russia, and possibly lead to a "nightmare domino effect" with other countries departing, he fears.

Mr Bielecki says the prime minister's best hope is to focus on the overall advantages of the European Union rather than letting his opponents sidetrack the debate into "marginal issues - including the Brussels deal".

"Step into the light"

Other commentators agree that the referendum has implications far beyond British politics.

The migration crisis could weigh on UK voters' minds in June, according to Frankfurter Allgemeine Zeitung

Jochen Buchsteiner in Germany's centre-right Frankfurter Allgemeine Zeitung notes that Conservative Brexit campaigners are pitching their appeal on the "primacy of national sovereignty".

They may well start asking whether Germany will demand concessions from Britain on refugees in return for the Brussels deal, which he says "owed much" to Chancellor Angela Merkel.

His concern is that a European Union still dominated by immigration, the euro crisis and "political helplessness" in June might persuade many voters that EU exit would not be a "leap in the dark" but rather a case of "stepping into the light".

Legal analyst Araceli Mangas also has concerns about the referendum, in Spain's conservative El Pais.

He writes that Britain remaining in the EU "matters a great deal", and a win for Brexit would "encourage all sorts of populists".

BBC Monitoring reports and analyses news from TV, radio, web and print media around the world. You can follow BBC Monitoring on Twitter and Facebook.