In the southern UK, by the end of May civil twilight ends 45 minutes after sunset, about 9 pm UT (10 pm BST). Although the sky is still quite light the brighter stars and planets will be coming into view. For most purposes the sky is dark when nautical twilight ends an hour or more later at this time of year. For deep sky viewing the sky is considered dark even later at the end of astronomical twilight. At the end of May UK skies are never out of astronomical twilight.
Viewing is limited to late night and the wee small hours in late May, June and July, the further north you go the shorter the darkness lasts. In the far north the sky never really gets dark at all by late May.
View south in May at 23:00 UT (24:00 BST) on the 1st, 22:00 UT on the 15th and 21:00 UT on the 29th
At the map times the southern sky is occupied by Leo, Virgo and Boötes whose brightest stars are Regulus, Spica and Arcturus respectively. Arcturus is an orange giant star 25 times the diameter of the Sun and the fourth brightest individual star in the sky. The arc formed by the handle of the Plough traces through Arcturus and then Spica. An even larger red giant star Antares is rising in Scorpius in the southeast.
Saturn is past opposition but still moving retrograde on the border of Libra and Virgo.
View north in May at 23:00 UT (23:00 BST) on the 1st, 22:00 UT on the 15th and 21:00 UT on the 29th
Looking north, constellations that were overhead in autumn and winter (Cassiopeia, Perseus and Auriga) now lie on the horizon. Castor and Pollux in Gemini are heading for the horizon but are never below it for long in the UK, especially in the far north.
Meanwhile Lyra and Cygnus with the bright stars Lyra and Deneb are rising in the northeast. They will become prominent in summer and autumn evenings. The bulk of our own galaxy, the Milky Way, runs just above the horizon through all these constellations and Scorpius, so is not very high in the sky at this time of year.
Images generated using Stellarium