Interesting premise - 'anomalies' popping up in diverse parts of London. These anomalies are naturally (one supposes) occurring portals to the past. The perfect plot devices - they remain for a limited time only. Just long enough for creatures to arrive and create a bit of mayhem. To date these have been prehistoric eras that ensure dinosaurs and other rabid fauna can come through and wreak havoc. We've had a diverse array of battling creatures that include giant centipedes, spiders and dodos. Yes, dodos. But, if you're looking for originality, you can stop reading and look elsewhere. Everything is game for these writers. Episode 4, with our rambunctious dodos, included hilarious thievery from Stargate, SG1.
The cast is adequate with stock characters. The suited bureaucrat who thrives on secrecy and SWAT teams; tousle haired professor who touts various theories; goofy geekoid student who insinuates himself into the proceedings. Et al. All moving under the premise, as with SG1, that all of this can be kept secret from a public sure to panic and riot if revealed. A rather more interesting character is the professor's long lost wife - found to be jumping among timelines and having the ability to predict where and when one will open.
But the bottom line is this: it's fun. It's not great, and it's not replete with originality. But you will probably go back each week for more. After all, what competition is there? Under these criteria I give it 6 out of 10.