If you refer to the Republic of Ireland pre-Euro Pound notes, you can only exchange them at the Central Bank in Dublin.
If you refer to the Northern Ireland Pound notes issued by any of the Northern Ireland retail banks, you should be able to exchange them at any English bank.
The first Bank of England Twenty Pound note was issued in 1725. The first Bank of England decimal Twenty Pound note was issued in 1970.
A currency exchange office can be found in most cities and airports, some hotels may exchange currency.
The short answer is no. The Elgar Twenty Pound note was withdrawn from circulation on 30-June-2010 and the grace period has long since expired. The Bank of England will always honour withdrawn banknotes. See the link below for instructions.
The Bank of England advises that the Sir Edward Elgar style Twenty Pound note was withdrawn on the 30th of June, 2010. After the 30th of June, most banks, building societies and Post Offices will accept the old notes for deposits and other transactions for a few months. Exchange of notes, other than for transactions and deposits is at the discretion of the institution concerned. There is no obligation on banks to accept the old notes. The Bank of England further advises that - Genuine Bank of England notes that have been withdrawn from circulation retain their face value for all time and can be exchanged at the Bank of England in London. There is no fee for this service. See the link below.
will the NatWest bank change my saved old 20 pound notes if I am one of their customers
You would be better off exchanging it at a foreign exchange centre, though it depends what bank you use.
Any bank will accept any Two Pound coin, they are legal tender.
Only at the central bank in Dublin.
The Bank of England currently issues Five Pound, Ten Pound, Twenty Pound and Fifty Pound notes for Britain, plus a variety of banknotes for a number of other countries.
You would have to pay them in to a bank (if you still can).
After a quick search I found a link for this one see Banknotes
No, The Irish pound is no longer a currency. The Irish pound ceased to be a full currency in 2002 when Ireland switched to the Euro. In order to turn these into usable currency they must be traded for Euro at the Irish Central Bank in Dublin. A local bank in Ireland should be able to assist you with this. Note however that due to their discontinuation, Irish banknotes will probably return a small premium if sold to a currency collector.