If time is a limiting factor, you are somewhat restricted from LGW. Dublin might be another option. However, I would recommend Paris CDG as a good option as there are frequent flights even on a weekend. If you could stretch to around £220 or so, Copenhagen is a good day out, departing at 0955 returing into Heathrow around 1700.

The flight to Paris is certainly longer than to Jersey and you will probably get a brand new A321 on one of your flights!

Amsterdam is another option which might be a possibility from LGW however I think the schedule on a weekend is quite poor with flights leaving early in the morning and returning late in the night.