Paris - London route other than Dieppe>Newhaven?

I had a trip planned for first weekend in Sept - late night ferry from Newhaven>Dieppe, cycle to Paris via Avenue Verte. Stay in cheap hotel on outskirts of Paris, then cycle back to Dieppe for late night ferry back.
This was all fine until I went to book ferry - outward trip fine, but no return ferry available. This seemed odd when presumably they can fit loads of bikes in. I emailed them seeing if something was wrong with the site and got the response: "The 3rd september is one of the busiest weekend of the year and priority is given to passengers with vehicule . We apologise not to succeed to your demand."
Which is really annoying...

So can anyone suggest any sensible alternative routes back? Obviously I could just get return Eurostar, but I resent paying more for something I don't really want to do. Plus last Eurostar of the day is at 9 which makes everything a bit more rushed than I really need it to be. Am guessing there isn't really a solution - cycle to Le Havre or Caen maybe. Really not keen on Calais having cycled out through there before. Can anyone think of anything clever I've not thought of (dates not flexible unfortunately)?

The answer to my question turned out to be - whine about it on the ferry company's Facebook and they might release some more bike spaces for the crossing in question. Which is what's happened. So back to original plan. Now just need to figure out which of the many Avenue Verte GPX files are best to use.

I might suggest the "whine about it on the ferry company's Facebook" option for my mates in The Fridays. We were unsuccessful getting more than 6 cycle spaces for on the Newhaven/Dieppe ferry back in July, even though there was more than enough spaces for bikes. Cars are more favoured during school holidays, apparently.

It is all bullshit. Have used that ferry a few times and the sections where the bikes go could fit a hundred bikes if they could be bothered.

Going as a foot passenger with a bike in pieces also works.

They really seem to favour cars. It's a good service in many ways and I can't complain about the journey out. But on the way back they made bikes wait to the very last for loading. Even though I'd arrived 2 hours early I had to stand in the cold inhaling diesel fumes while every other vehicle boarded. They let all the motorbikes on right at the start which go into the same area as bikes, so it didn't really make any sense.

Was great aside from that - did Donald Hirsch route out, proper Avenue Verte back, both were really good (assuming you don't mind the odd bit of off-road). But after a long ride, standing around in the cold isn't what you want to do. If I'd known, I'd have just stayed in the centre of Dieppe drinking and eating until the last minute.

Ferry companies seem to be hit and miss in how they treat cyclists. On my recent trip we were the last ones off the ferry in Dover, even though it wouldn't have delayed them to let us off first, as the cars/lorries went straight into a traffic jam.

I think Stena Lines is the only ferry company I've used that was totally great. But their routes aren't as useful.