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I'm not sure, to be honest.
If you need to register a child an a UK citizen, you need to have records from 5 years before their birth, so in my case over 10 years. I luckily have all that.
But other people in work just sent 5 years of proof for the past 5 years, if you have to get your qualifying period backdated to 10 years, yeah you do.
There's a good forum on facebook for questions if your acquaintance has questions. https://www.facebook.com/groups/132887737155325/
https://www.theguardian.com/politics/2017/may/07/british-at-last-dutch-woman-horrified-loss-rights-monique-hawkins
So, this came up before in this thread.
The HO has made getting permanent resident easier, if you work and have p60s for 5 years/haven't been out of the country it's now simpler.
BUT you lose EU national rights if you get British citizenship, you can't bring family over easily. This was brought in by Theresa May (well, who else, that friend of immigrants) so again having citizenship is not a panacea.
And not all of us can hold dual nationality. I can't. There's also an incredible backlog on processing PR applications, so the mess is not sorted yet.