4 week sailing itinerary

imagine you have a 4 week charter, so you have to start & finish in the same base, where would you go?

this isn't a fantasy question, we're thinking of doing it and would like suggestions/ ideas please; season isn't an issue but would obviously be outside hurricane season.

Some suggestions
I'd either start in Martinque or St. Lucia, depending on cost and ease of travel. Head north as far as Dominica stopping at Martinique (If starting in St. Lucia), les isles de saintes and Guadeloupe. Then providing the charter company allows you to sail at night, id head straight for Grenada then work my way back stopping at Carriacou and through the Grenadines. A 10 day/ 20 day split would allow plenty of time.
Alternatively the islands around Greece are also very nice and it would be easy to put together a R/T itinerary.
You could also consider the South Pacific, based out of say Tahiti and explore the surrounding area. Travel costs will might be a concern though. I haven't sailed in the South Pacific yet, leaving this Saturday for a 7 month charter, but it looks beautiful

I've done 8 weeks in Leeward Islands on a charter (out of Tortola and as far south as Iles des Saintes Guadeloupe and return) and am currently planning 2.5 weeks this June out of Martinique down to northern Grenadines and back. So with 4 weeks you can cover plenty of ground in Caribbean. It really just depends upon what type of cruising and environment you are looking for. Seeing you are out of London, I can't comment on the Med but obviously, the Caribbean is easy travel from there.

If it were me with 4 weeks, I'd probably cruise between St Martin down to Domenica and back, hitting nearly all islands in between. Much also depends on how much you like being on the go vs sitting in one place/island. I'm also assuming a R/T charter, and not one way since those can often be more challenging to arrange.

PS - the charter company will almost certainly not permit you to travel at night. Screw that but obviously you need the experience, training, gear, weather knowledge, and common sense to cover that.