If you're planning a trip to India before the end of the year make sure to pack any 500 or 1,000 rupee notes that you've been keeping hold of – because the notes will become worthless unless you exchange them in the country before 30 December.

The Indian government withdrew all 500 and 1,000 rupee notes yesterday, essentially leaving millions of people with invalid cash in their wallets. The move is designed to combat "the incidence of fake Indian currency notes in higher denominations" which are being "used for antinational and illegal activities," according to the Reserve Bank of India.

The withdrawn notes are worth around £6 and £12 at today's exchange rates.

For a few days, the old notes can be used at hospitals, petrol stations, crematoria and for other businesses and services deemed essential.

They can be exchanged for cash or deposited into accounts at banks and some post offices in India until Friday December 30. Customers can exchange any number of notes but will only receive up to 4,000 rupees in cash. Any value above this won't be issued in cash – it'll be paid into a bank account.

The Indian government is planning to issue brand new bank notes of 500 and 2,000 rupee denominations soon.

I've got 500 and 1,000 rupee notes but I'm in the UK – what can I do?

If you have withdrawn notes in this country, your options are unfortunately limited. The State Bank of India says it doesn't accept rupee notes at its UK branches. Neither do the Punjab National Bank or ICICI Bank – two other Indian banks with UK branches.

MoneySavingExpert.com has yet to find a way of exchanging the withdrawn notes in the UK, but is continuing to investigate the problem.

If you're planning to visit India before the end of the year, you can take your notes with you and exchange them. Another option is to transport them to India via a trusted friend or relative who's visiting in the coming weeks.

The Reserve Bank Of India says that if your notes are in India you can provide written authorisation for someone there to deposit them in your bank account.

Your designated person must attend a bank with the authority letter given by you, and a valid proof of identity (a list of acceptable ones is in its FAQs).

We've heard of at least one UK resident asking friends to take their money over so relatives can bank it on their behalf.

However, if you're planning on doing this, be careful – there are rules about how many rupees you can take in and out of India.

In 2014 the Reserve Bank of India declared that all residents and non-residents of India (except citizens of Pakistan and Bangladesh or those coming from/going to those countries) can take up to 25,000 rupees in and out the country.