This Summer 's Heatwave

Despite all the sophisticated equipment, weather can only be forecast accurately for the the next 48 hours and after that it is a best guess based on probability on conditions that could change so to ask a weatherman if the below average temperatures for May is a sign that summer isn't going to be
as oppressively hot as last year when the record 40.3C was hit in July, is met with a shrug and a 'dunno'.
What we do know is that Summer is on it's way and the temperatures will rise so the MET Office modelling system takes all the information from recent historical data, global weather, La Niña, the effects of climate change and the typical conditions we'd normally expect to create a seasonal outlook and present the probability of weather conditions for May to July.
The temperature outlook for May to July 2023 is that there is a 5% chance this period will be cool, a 60% chance it will be near average and a 35% that it will be hot so based on that, the best chance is we can expect average temperatures in this period with a much greater chance of it turning out warmer (35%) as opposed to cooler (5%) than normal.  
As for if we are due to get a heatwave, that depends on where you live in the country as a heatwave is three consecutive days above 25°C in Scotland and Northern Ireland and between 26°C and 28°C in the rest of the UK.   
What this all means is we can expect a average or above average temperatures this summer and you will need to check your weather app to see which days are going to be average or above average but it is unlikely we will break any heat records this year.
The MET Office state that the 40.3°C of last year was a once every 1000 years event but as the climate continues to warm and weather records tumble, we are finding that these weather events are happening alarmingly less than once a millennium now.