Went to Welsh-speaking schools.
Names that were very popular were:
Bethan, Siân, Carys, Nia, Rhian, Delyth, Sioned, Eleri, Catrin, Llinos, Eirian, Ann. Some of these seem middle-aged now because they are mums' names and I know so many.
Boys names that are now dads' names:
Dylan, Dewi, Gareth, Huw, John, Siôn, Alun, Aled, Dafydd, Iwan, Geraint, Gethin, Bryn, Rhys, Glyn.
Of the fellow pupils that didn't have Welsh names, the following seem to not be current baby names:
David, Mark, Stephen, Ian, Darren, Wayne, Paul, Alan, Richard, Nick, Chris, Simon, Gary, Andrew.
Sarah, Karen, Susan, Joanne, Suzanne, Sharon, Tracey, Linda, Paula, Mandy, Debbie, Michelle, Ruth, Nicola, Lindsay, Julie, Rachel, Clare, Rebecca, Victoria, Gillian, Carol, Catherine, Kathryn, Kirstie, Helen.
Some were beginning to get popular and some were past their peak. Some of them are due for a revival, and some are still used, but some seem dated.
Probably not representative of UK.