If you can reach it from the ground, a large piece of cardboard, such as a flattened carboard box, as Tigercub says, would do if you can wedge it with a ladder or something to prevent it blowing away. You only need to protect it during the first night. The bricks will hold enough heat that the surface will not be frosted unless it is exposed to a clear night sky or a very cold wind. After the first night it will have enough strength to resist frost damage.
If the night is mild, clouded and rainy, it will be OK anyway. Cloudy, drizzly weather is ideal for new concrete and mortar.
Thanks everyone for your replies, wasn't expecting such drama
In the end I did put up some protective covering of sorts to be on the safe side, but sounds like there's more important stuff to worry about than this
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local