Have just updated our UK wills and have included the Brussels 4 declaration which states our estate is to be administered under UK inheritance rules. Is it necessary to have these translated and notarised in Portugal?

A UK will has no jurisdiction in the EU anymore than a French or Portugese will has no jurisdiction in the UK.This is particularly relevant in respect of "real property" ie land houses etc in another country.Also many financial institutions will not recognise a will made in another country.
IMO you will need to make a Portugese will especially if you have property in Portugal and then add the declaration to that will.I know in French law there can be inheritance problems for spouses especially second ones if no will is made but I am sure someone will be along to explain the default inheritance rules in PT. Also the Brussels 4 declaration does not affect any inheritance tax liability in the EU.
Being a pedant there are no UK inheritance rules.Scotland and NI have different rules to England and Wales

Just done some digging and appears contrary to the reply above, that a UK will can be valid in Portugal. See - Wills in Portugal (judicaregroup.com) Will have a word with the notary we've used before to get advice, when we return.

Thank you for posting that link. Very helpful.

Well i have learnt something-but reading the info leaflet it actually advises that the best way to proceed is to make a Portugese will as it is cheaper than getting a translation of the uk will and quicker.And remember whoever you leave behind will be dealing with this so it may be easier to have the notary deal with the portugese end .Just as an aside we have made up a "death pack" and left it with a trusted relative in the case of our demise which contains all our bank details energy suppliers etc etc.You never know what is the round the corner so it pays to prepare things.

A death pack is an excellent idea.

We've also left instructions in the UK and in Portugal, listing our solicitors etc. We still have our main home in UK, plus an apartment and boat in Portugal. To make matters more complicated, my wife's citizen card and apartment ownership docs are in her maiden name whereas UK house and boat are under married name, as is her UK passport. Everything we have is in joint ownership. We don't have any children so, after we've both snuffed it, estate will be split between various family members of both nationalities living in both countries, .There can't be two "last" wills in effect at the same time so it's going to be pretty complicated to sort out to avoid one possibly overriding the other.

So... can a notary do this rather than a solicitor? We have translated our UK will (OH is a PT) but I suppose it might need a bit of legal gobbledegook so may not pass muster. Keep putting this off as its a minefield, and I keep getting different advice on what should be done, but time is getting on and when we are there again we MUST DO IT!! Sort of started a death pack .Leaving info in both properties re solicitors ,accounts etc. Like Graham F we've no kids,and I shudder to think what will happen to our stuff and its worth when we kick the bucket, as we havn't anyone to supervise who is doing what!! (not got a lot of trust in the legal system and those who work in it). Proceeds all to charities so would hope they get their money.

There's a very useful template here for the legal goggledeguck:
https://pdfexpert.com/pt/last-will-template
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There's some more information here. EUR-Lex - jl0070 - EN - EUR-Lex (europa.eu) It seems we need a European Certificate of Succession to be used by heirs, legatees, executors of wills or administrators of the estate to demonstrate their status and/or exercise their rights or powers in another EU country.

Anyway, rather than possibly making a mess of it, we'll be obtaining legal advice in Portugal.

I suspect if that form were filled in, Portuguese laws of inheritance would apply to anyone resident there, which is the last thing we want for our circumstances. Inheritance is dictated by law so, when my father-in-law died, we had the usual situation,where estate was divided between mother-in-law and children. As my brother-in-law had died, his share was divided between his children, one of whom was illegitimate but still treated equally. When mother-in-law died some years later, everything went to children and grand children. All beneficiaries had to agree before property was sold.

I believe this might be Brazilian? The pt referred to in the title is just for the language portuguese - otherwise references are all to Brazil and Brazilian?