That would take too much time buddy
look for the snap eurostar offer or buses.
If you have flexibility try standby on some of the cheap carriers that fly back and forth. You can fly really cheap when they are trying to fill seats.
Yes, as #4 says, check out the Eurostar Snap fares. See here for details:
You need to buy them at least 7 days in advance and you do not get to specify a train, only morning or afternoon and they assign you a train, so it only works if your schedule is flexible. Fares are 25 GBP I believe.
Also, there is still reasonably inexpensive airfare available on some LCCs, but the cheapest fares probably do not include hold luggage so you have to factor that in, plus the cost of travel to and from the airports in question.
Those seem the most reasonable options. Otherwise there's a very long bus ride for something like 15 EUR I guess.
If time is a real issue you could run, swim, run 😆