Grrr Leo was doing so well with his housetraining, he hasnt made a mess in any house for over a week, then yesterday it starts raining and he makes a mess in the kitchen twice, we take him to my parents and while i leave him with my dad he does it there twice.
If we take him out he runs to get back in, or eventually he goes but doesnt like being out there at all. He's being sneaky and doing where he thinks we cant see him.

We are back to taking him out all the time, whereas we were so proud of him going by himself everywhere before.

Any tips on getting him to go out when its raining?

There's no easy option here I've found, especially toilet training my 2 Staff boys over the winter, they loathe the rain.  I took them outside, and spent much time sheltering under an umbrella or getting wet myself and they did eventually learn that the quicker they had a wee or whatever the quicker they came back in again.  If they didn't perform in a few minutes, then I brought them in, watched them like a hawk and took them out again 20 minutes later or if they showed signs of squatting indoors somewhere.  The minute they performed then they got a ridiculous amount of praise.  It took huge amounts of patience but 8 months on, they will go out in the rain, run down the garden, do their business in lightning quick time and race back indoors.  Just keep at it, unfortunately, you can't avoid taking them out in the rain and they just have to get used to it! :-)

dogs are so shallow lol - if hes going for a walk he doesnt mind the rain lol

OOOH progress we just sent him outside in the rain and he left us a little present and did 2 wees, maybe hes been storing it up all morning

Funnily enough, my lot are very happy to go out in the rain for a walk too!  BTW, you don't say how old Leo is, but if he's only gone one week being clean in the house, then I guess he is still yet very young, so don't worry too much, a lot of pups regress from time to time with their toilet training, regardless of whether it's raining or not!  One of my Staff boys only really has been housetrained in the last few weeks and even now I still don't fully trust him but his litter brother has been an angel to housetrain; some are brilliant some are not.  But it sounds like you're doing ok and this is only a very minor setback and totally understandable in a pup.

I understand totally hes only 15 weeks, we didnt get him until teh day before he was 11 weeks so we lost a few weeks. But in the last week he had totally changed, hes been ok in or house for a while but in the last week at the office he was letting himself out, at my parents he let himself out and we even took him to a house he hadnt been too before and he went straight off looking for something that looked like a back door.

The most frustrating is OH's parents, they wont let him walk thru the house, hes chucked straight in the garden and she makes us sit outside all day in the freezing cold "incase he has an accident" and i will be so happy the day she finally allows him in the house lol.

Hes a good boy in general tho, we introduced him to a kong the other day and he loved it, he seems to think he should have all meals in it because its more fun that his bowl an dhe gets cheese spread in the kong lol.
He's sitting next to me at the moment chewing his toys, i give him 5 mins before he comes and stands on my laptop to say he wants a cuddle.

Blimey, 15 wks old and almost clean, I'm deeply envious of you...took one of my Staff boys about 7 mths to get to that stage! :-)

Can't remember what breed Leo is but some breeds apparently are significantly easier to train than others so you may also have to bear that in mind if there are odd relapses, but to be honest, I think any breed can relapse and just have amnesia when it comes to squatting suddenly in the house.  In the case of my Staff, he just thought housetraining happened to his brother and not to him! :-)

He sounds like he has a lovely life with you and just keep up the good work so far, you must be very proud of him...

I used to have a Mini Schnauzer who when sent into the garden to 'be clean' in the rain only ever walked on three legs.
She carried the left back one off the ground putting it down again as soon as she came back in the house.
I guess she was keeping it dry. :-D