SS81

Hi, I'm UK citizen and tax payer. My sister has been living as a permanent resident in Australia for 19 years and is now planning to move back home to the UK. She wants to transfer a large sum of money, around £400,000 to me now to hold until she gets home in 3 months as the exchange rate is getting worse and then I will transfer this back to her once she is home and has a UK bank account set up. Is thus permitted and are their tax implications for me if I am receiving this large amount even only to hold temporarily?