Are british people these days mostly of ancient british ancestry?

We have had waves of conquerers since ancient British times, Roman,s Saxons, Vikings, and Normans. We have also had influxes of immigrants, like large numbers of Huguenots in the 17th century for example. Mingling of races has gone on ever since then. I would be surprised if there is anyone of English descent who hasn't got some ancient British in them, but I think any quest to find 'true Britons' is doomed to failure, because I doubt there is anyone alive in Britain who isn't a bit of a mixture.