By Bradley Jolly The Met Office has told the Mirror pollen levels will be high for most of the country this week. Temperatures are set to increase throughout the week, peaking at 26C in the south of the UK on Saturday, but the pleasant warmth causes plants to release pollen. Oak and birch are the typical culprits this time of the year but the Met Office forecasts levels of all pollen, including grass, to be high across the country this week. Thursday will be the worst day for hayfever sufferers as levels will be high as far north as Northumbria, and as far south as Cornwall. All regions of Nor…