Is over 33.5C possible Thurs? Yes! 34.1C

Update 20Z   34.1C max. at Heathrow today  reported by UK Met Office

Hot air is over the southern UK today and forecasts show the possibility for over 33C. One useful forecasting tool is thickness lines1000-500hPa (and 1000-850hPa). These contour lines show the different heights/thicknesses of 2 pressure levels. Warmer air being 'thicker', less dense. In winter, the 528 thickness line is a good rule of thumb for the potential for snow, rather than rain.

The thickness charts for this afternoon, do show the highest values so far this year, so inland England could beat 33.5C.
Currently, the 570 line (100-500hPa) is well over central and SE England, allowing these areas to heat up to near 30C. The hottest part of the day is normally mid/late afternoon. Looking at the thickness charts, a tongue of 573 creeps over Kent this evening, so that doesn't coincide with the peak of sunshine heat in the day. Looking at the 850-100hPa contours, there is a higher value area at 15Z into London, Beds. Cambs. and Herts. The 1425 line comes into the south coast at 17Z, it will feel hot and humid here by this evening.

The all time UK record is 38.5C, so still a way off