The Beeb/MetOffice only has temps peaking between 24/26C locally on Sat/Sun/Mon, with a high chance of thundery showers/storms thrown in for fun, so not overly hot - except maybe for the east and south-east, despite the country wide warnings this morning.
Have a mighty 11.5C here now, so the BBC's to even forecast 18C is a complete pi** take on their ability to forecast accurately, so the weekend and 26/27C may well be another disappointment.
May of posted this website before, plenty of interesting charts to keep you occupied during this major event awaiting to hit our shores - www.weathercharts.org.