From 1st October the UKIPO will not be rejecting trade marks if there is already a potentially-conflicting mark on the register ("relative grounds"). They will still reject inherently unacceptable marks ("absolute grounds") – ie not distinctive, descriptive of goods or service, offensive and so on. Instead they will tell the applicant and the holders of the previous mark(s) about any potential conflicts and leave it to them to negotiate a solution or fight out an opposition action. This is because the EC Community Trade Marks are not examined for conflict at all and applicants were unhappy about having their British trade marks rejected over EC marks which did not have to face that hurdle.
They will inform the holders of potentially-conflicting earlier British marks and Madrid marks with Britain as designated state automatically. However, holders of EC marks and Madrid marks designating the international EC scheme will only be notified if the holder has informed the UKIPO that they wish to be notified. This is a charged service and they have to register using a web form that will be put onto the UKIPO web site on 1st October. So that the site doesn't collapse under a rush, holders of EC or Madrid (EC) marks have until 20th October to register before the first batch of notifications go out. The potentially-conflicting earlier marks will be visible in the entry for the new application on the free UKIPO trade mark status database, but there will not initially be any reference to the conflict on the status page for the earlier mark (apparently there has been some demand for this in the meetings and it may be introduced later).
Under the new rules nobody will be able to bring an opposition action (a legal action to oppose the grant of a trade mark on the grounds of a conflicting prior mark) except the proprietor of the prior mark. For oppositions based on existing unregistered marks, anybody who would have the right to bring an action for common law passing off to defend the mark will also have the right to bring an opposition. Licensees of the earlier mark will only be able to oppose by bringing the action in the name of the proprietor with their permission ("intervention") but they will be able to bring an invalidation action after the mark is granted without this being necessary.
Current legal opinion is that any proprietor of an older mark who does not immediately oppose the grant of a conflicting application will not be prevented from bringing an action later by either the laches or acquiescence rules (whatever they are).