Filling around gutter downpipe drain

[zerodefect]

I had my drive tarmaced about 3 years ago. I've recently noticed that small cavities have emerged around one of the drains. It looks like the drain is a bit cracked now too.

My biggest concern is subsidence as water from the sloped drive does flow in the direction of the drain and the drain is positioned near the external wall of the house. To be exact, I'm concerned about the water going down through the cavities on the side of the drain. I noticed today that an army of ants have started making the drain their home too.

The cavities are smallish, but larger than they appear in the photos. I thought about putting hydraulic cement down there, but if i recall the consistency is quite thick? The other thing to do is rip up the whole lot. Do I risk subsidence?

I have attached photos of the drain. It's difficult to get in at a good angle near the wall to take a photo because of the tight space.

 

[foxhole]

Pour some bitumen in to seal and also strengthen the cracked pipe. The down pipe should have a cap around the base to prevent debri being washed in.