As you've missed the entrance exam you won't get a place when offers come out in March. You may get a place via the waiting list. However, if your child takes the test, passes and would have got a place had you not missed the deadline, I think you have a decent case for appeal. I will be happy to help you with this.
To outline the argument, the national closing date for applications for secondary schools is 31st October. There is no scope in the Admissions Code for admission authorities to set their own closing date, but that is, in effect, what Urmston has done. They accept applications from the beginning of June according to their admission arrangements (however, the timetable on their website suggests they actually accepted applications from 9th May) and set a closing date of 24th June (not mentioned in their admission arrangements), so the window for applications is quite short. Anyone applying after this date will not be allowed to sit the entrance test and will not, therefore, be able to get a place. So they are operating a closing date of 24th June - over 4 months before the national closing date. Given that the tests do not actually take place until 19th September, that seems ridiculously early. Further, it is clearly contrary to the national closing date.
Urmston may argue that they are required to inform parents of the outcome of the admission tests before the national closing date, but that is wrong. They are only required to make best efforts to do so, in order that parents whose child has not passed the test don't waste one of their preferences. There is nothing in the admissions code that prevents them from notifying parents of the result after the closing date if it was not possible to do so before.
Some other selective schools get this right. They run tests before the closing date but then run further tests after the closing date for those that missed the initial tests. That way, everyone who applies by the national closing date for offers gets tested and, if they pass, has a chance of getting a place.
In my view, Urmston's admission arrangements are contrary to the Admissions Code. I can't guarantee that an appeal panel would agree, but I will be happy to help you put the argument if you want to go down that path.