You can view roaming charges for Greece at https://ee.co.uk/help/mobile/roaming/roaming-costs
As per the results on that page, you may either pay a daily charge of £2.29 to use your UK allowances, or a monthly charge of £25/month. 7 days x £2.29 is a cheaper option for you.
Remember to text ROAMING to 150 before leaving the UK, this ensures your phone is setup to connect to foreign networks, now & in the future.
