Thanks for all the suggestions! I'm not quite sure her reasoning is coming on fast enough to do all of these yet (eg. doesnt know what a police man is yet) but I may try the hair clip if I can find one, or try to source the chest strap. I was going to try the "stop the car" one today and set big sister watching for escape attempts, but DD1 missed it and told me after we had arrived that DD2 had done it again. Unfortunately she seems able to free her hands even when I pull the straps with all my strength.

My 8 year old did this.  I took her to Babies R Us, and put her in the display carseats and stood back and waited, she was able to get out of 7 of them, I had the store manager come up and ask me what I was doing, I told him if she cant get out of one I will buy it, and he said children her age cant get out, she was about 19 months, so he was shocked when she did.  I bought the 8th car seat we tried, because she couldnt get out of it.  We had an audience for the last 4 seats.  I know they are expensive, but isnt your child worth it?  So maybe try that, as to the diaper pin idea previously posted that could be dangerous in an accident, or even if you have to slam on the brakes, it could pop open and poke your child.  good luck! 

My sister used to do this as a baby.  I remember my parents resorting to a hair clip in order to stop her from getting lose.  One of those long hair clips that have those painful clasps on them.  it worked a treat.

My son has done this a couple of times and I've told him that he cannot do it because it isn't safe. And for one, a police man may stop us and get mad at me for not keeping him safe. This works of course because policemen is one of the things he is very interested in. Also, I've threatened him that I will stop in the side of the road - this works too because I did it once (for another reason) and he didn't like it. :-)

this happened to my friend. she would tighten the belts but her son still got out of them.  he actually fell out of the seat when she stopped one day and he hasnt done it since.  just keep on telling her its naughty or get a police officer to tell her its naughty.

I've definitely used the "stop the car" technique with my girls.  I warn them ahead of time, and then if they do it, I stop the car and get the seatbelt sorted out before driving again.  I'm also wondering if the seat belt might need to be a touch tighter so she doesn't have so much slippage room to get her arms out (mind you - kids seem to be mini-Houdinis!).

At 22 months I don't know if other forms of punishment or bribery might work (I'll take your teddy bear for the remainder of the trip if you take your arms out; or You can play with the playdough when we get home if you're good), but it depends on the level of reasoning of your child.

Best of luck!

Bella's done it a couple of times, so I now watch her in the rear vision mirror and if she does it, I stop the car immediately, tell her off and put her arms back in (& tighten it).  Don't know if that helps, but I think the immediacy of "oh, why has mummy stopped the car" seems to shock her into not doing it.

Perhaps you could make her responsible for making sure that everyone has their seatbelt on... Also, tie a teddy or dolly to a chair and pretend it is their seatbelt and they tip forward in a hard breaking situation.  Untie teddy or dolly and tip them forward in the same situation; they hit the floor OUCH! 

We only had this situation twice, now we can't even start moving the car without a massive lecture if someone isn't wearing their seatbelt.  Another solution is to get a little belt tie thingy that goes across their chest, though I am not sure if you can source them in the uk... You can see in a couple of these pictures that the kids are wearing them.

AHH!!!  I have a solution!!  All my kids did the same thing.  The trick is to use a diaper pin (the kind for cloth diapers), and pin the belts together at the top of the childs chest.  This way, the child can't see well enough to undo the pin, and they get awful tired trying to figure it out blind.  Worked every time!!!

I read somewhere that you can buy a part that holds the shoulder straps together. This might be worth looking into.

My boys were both older when they started doing this and were able to put their arms back in most of the time so we'd just stop the car and wait until they did it. We also tried to be very positive if they made a car trip without doing it. Eventually they stopped.