We're in a very multicultural area so duplication really isn't a major thing here as there's such a massive range of names. I often think 3 kids in a class with the same name is a bit of an urban myth these days as I honestly have never experienced it in over 15 years of teaching. Maybe it's a rural (white) leafy village thing?
The names I've taught the most of in recent years (Reception, so all the kids are now 4-10ish) are Sophia/Sofia, Olivia, Maya, Eva, Jessica, Maryam, Noah, Lucas, Caleb, David, Adam, Oscar, Archie (so mainly names which generally appeal to people across multiple different cultures and nationalities, baring the odd exception). Muhammed/Mohammed too technically if going by birth name, although none of the ones I have taught have actually gone by that name as it's their father or grandfather's name so they've gone by middle names (Hussain, Abubakar, Sajid etc).
At the start of my teaching career, the popular names were Lily, Ella, Grace, Ruby, Victoria, Lucy, Sophie, Anya, Jack, Ethan, Thomas, Ryan, Daniel, Jayden but they're teenagers now and a lot of those seem to be less in favour these days.
My eldest doesn't have any duplicates in her class (one entry primary) but Noah, Thomas, Charlie, Oscar, Alfie, Ravi, Isla, Olivia, Sienna, Esme and Evelyn are all repeated at least once throughout the school, of the kids I know.
My youngest is at nursery and they have a few girls called Harper, Luna and Aliyah throughout the different age groups. Freddie, Penelope/Penny, Aria, Mila and Isla are also very popular at the various groups we go to.