Several thousand people are taking part in a demonstration in Warsaw organised by Polish nationalist groups against mass immigration. The first round of the presidential election will take place in a week's time, and the pro-European mayor of Warsaw, Rafal Trzaskowski, is leading in the polls ahead of Karol Nawrocki, supported by the nationalist Law and Justice Party (PiS), and Slawomir Mentzen, candidate of the Confederation, a far-right libertarian party. IMAGES AND SOUNDBITES