Yes Bluebell it is a worry. I nearly lost some lettuce which I planted last Saturday, then covered with fleece to stop blackbirds scuffing the compost, then watered them in and watered again after three days, but by day six some were brown at the edges = very dry! A good soak and fleece replaced by netting over cloche hoops has restored their health and if you have enough water to wet soil before planting, then water in after planting, plants should survive a three day interval until their roots are established further down.
The heat is much stronger than we are used to so give more water than you would normally. I am watering tomatoes undercover (in soil) every two days, a good soak.