If you become member of parliament you can get out. In fact I believe you just have to stand, but don't quote me on that.
.. used to be (until late 70s??) that just standing worked.
Then many realised a deposit was cheaper than "buying yourself out". So rules changed, and you have to be elected.
Doesn't help the OP, but I don't think that's quite right. Before becoming a parliamentary candidate you have to apply to retire or resign or be granted a free discharge.
Whether your application is granted or not will depend on the exigencies of the service.
Having been allowed to retire etc, an unsuccessful parliamentary candidate has no right of reinstatement - or duty to return, for that matter. See QRs.