Intellectual properrty?? Can my ex boss use my ideas?

Theoretically if you put in a proposal for a job that is detaild and they go on to use all your ideas but do not hire you is it theft of intellectual property or just bad luck.

You said "but do not hire you" in your question. Can we take that to mean that you were attempting to establish a contractual relationship with this company? If you were paid by the company, then they own the product of your work. There is a potential (practical) course that you can follow, but the results are going to depend on having a good intellectual property specialist on your side. I suggest trying to get with a good lawyer who knows intellectual property and discuss your situation in detail. You may find that you can extract some kind of compensation even though your intellectual property claims may not be as strong as you would like.

always copyright first before you do this.

Just bad luck. They were paying you when you came up with the idea. They own it.

ethical? no
legal? yes.

so you didn't get the job? if it's not protected then you're sol. you learned the hard way never to disclose info before you get what you want.

My contract of employment states quite clearly that anything I create whilst at work belongs to my employer.

Any idea you have while working for a company belongs to the company that employs you. If however you have an idea and leave the company to create a start up and sell the idea, the idea is yours.

In your particular case, it seems like it is bad luck; If at your interview, the prospective employer decided to use your idea, to stop them, you would have to have some protections in place such as a copyright (which is automatic on pretty much anything you publish, or print) or a patent. For an idea though, you really need a patent in place otherwise there is not much to stop someone else exploiting your inventions. A patent is basically the right to exclude others from using your idea.

If you came up with an idea while employed by an organisation, they have the moral and intellectual rights to your output. Your payment is the salary you earned.

Most employers make employees sign a declaration which assigns IP ownership rights of any inventions which they make whilst employed by the company, whether or not the invention is made during working hours, and whether or not the invention is related to the business of the employer. Many empoyers will agree to give back ownership of ideas which are clearly unrelated. For example if you work for a company which makes mobile phones, and at the weekend on your small farm you think of a great new gadget for feeding pigs, then usually the employer will agree to let you have the ownership rights (unless of course they also have another division making pigfeeding equipment ;-) )

Where such an IP assignment does not exist, then your ideas are only protected once you protect them. Before discussing them with ANYONE, you must either register your ideas (in the form of a patent), or you must enter into a confidentiality agreement (Non-Disclosure Agreement or NDA) in which the other person agrees not to use your ideas or discuss them with anyone else. If you tell anyone your ideas without such an agreement in place then you are putting them in the public domain, and it is not consider "theft" if they use them.