Honestly the best thing to do with them is give them to charity!!! I would keep the biggest pair that you own as an inspiration to keep going, but the rest...get rid of!! That way if you do stick on a bit of weight, you can't just fall into the trap of getting your "fat" clothes (sorry if that term offends anyone, but that is what I call mine), back on and then keep gaining....If you give them away, as your new clothes may feel a bit of a pull, you have 2 choices...either kick-start your weight loss or actually go out and buy bigger clothes again!!
By the way Dozzy...Woohoo on them being too loose!!!! Well done mate!! Feels good doesn't it???