Be very careful before signing any new contract since you might be "jumping out of the frying pan into the fire", as the saying goes. Also, be sure of your rights...much depends on how long you have worked for your present employer insofar as payment of compensation is concerned. If you are "dismissed" as a result of the merger of your employer's company you will have the right of appeal to an industrial tribunal since this course of action would involve only yourself and no-ene else at the company. In other words, it would be foolhardy of your employer to "dismiss" every employee on his/her books since every one could conceivably appeal to a tribunal independently thus involving the employer in whosesale financial risk. On the other hand, your employer may decide on a policy of "redundancy", a protracted procedure which involves the position you currently hold at the firm and not merely you as an individual, so any number of other employees are also at risk of losing their jobs, and in this instance, your Trade Union should be consulted at an early stage.
If you are unhappy with your current situation at work, and you are wanting to leave of your own accord, then there is simply nothing you can do with regard to appeal or pursuing compensation, unless of course your state of unhappiness is as a result of some discrimination or harrassment towards you by your employer.
I have attempted to explain this highly complex issue on employment law as simply as possible, so I hope I have at least been helpful to some degree. But...don't act in haste or too rashly, you would do well to seek professional advice on a face-to-face encounter with a Solicitor.
Best wishes.