Hi Myrna,
Getting professional help is recommended for any tax-related issues. I can certainly point you in the direction of the right people.
As for getting taxed twice, there are double taxation treaties between the UK and Portugal to prevent this. When you go get that professional help, it’s worth asking about the NHR scheme which in many cases allows you to be taxed at source (i.e. the UK) rather than in Portugal.
The D7 sounds like the right route for you to go down as well.