Please try the following steps to import your emails from your Tesco account to your Gmail account:
·First of all, download Mozilla Thunderbird and install from https://www.thunderbird.net/en-US/
·Once the installation is complete go to “File” then “New” and “Existing Mail Account”
·Enter your credential information for your Tesco account.
·Repeat the steps for your Gmail account.
·Once you have both accounts set-up you will be able to drag the emails in ·Thunderbird from your Tesco account into your Gmail Account.
·The emails should now appear in your online Gmail email account.