What happens when the parties have reached the end of collective bargaining without reaching agreement?

Hi

I've been reading around the subject of trade unions and collective bargaining agreements. There seems to be a clear process to follow if the method of collective bargaining is not agreed between an employer and a union. What I am not clear about is what happens if no agreement is reached after that method is followed i.e. if a method is agreed and followed but the trade union and the employer fail to agree on an issue of wages, hours etc…what rights do the trade union and the employer have? Will such circumstances normally be covered in the collective bargaining agreement? Can the employer go ahead and implement whatever wage/hour issue is being discussed anyway because the bargaining has failed? Does a third party (Acas?) have to be brought in to mediate? Can the trade union members strike?

Any guidance would be appreciated.