It's usually something you have to set up with your mail server, which for you looks like it's the same as your ISP (tesco).
If it were something that your could do from whatever you use to read email, you'd have to have a computer on, with the program open and not set to hibernate or anything if it were left unused. Sometimes, you input the information through your email program, but it will be sending info off the the server and not all servers run on the same thing, or accept the particular settings.
I'd suggest going to the website for your ISP and searching for terms such as "holiday message", or "vacation message". However I'll add the same caution as others, this is really something better kept away from home, it's a very useful thing to have it set up on a work email account, with details as who to talk to if it's urgent and so on.
Cheers Anne