New cabinet 25 metres from an old one - on green space

Openreach won't be installing any new cabinets as all their splitters and fibre distribution goes underground.

If that is public land then your local council will have been informed of the plans to site a cabinet there and presumably didn't object which is why it's there now.

Yes indeed I do know why the additional cabinet is there. It's for their full fibre overlay network. Customer connections will go to the cabinet in the verge then on their merry way to a bigger cabinet where the optical connections all terminate. That will be a pair of cabinets, one larger and one smaller, elsewhere.

Looks like there's a cable network chamber in that grassy area already and they built the new cabinet and chamber over existing ducts. The full fibre cabinets tend to be smaller and carry fewer connections than the big old school cabinets so an area may need more of them. 

The smaller cabinet next to the existing one is potentially where a number of the cabinets like the one in the verge are aggregated on their way back to the termination point for the full fibre network. 

We also have VM street cabinets that are of the same size but painted grey.
Each of these small PON cabinet serves perhaps 24 homes.

The smaller cabinet serves a maximum 64 customers, more than the capacity of a standard tap block in the HFC cabinet it replaces. The larger cabinet has capacity for 500 connections. These are more likely to be put in where an existing HFC cabinet cannot have PON placed next to it (replacing more than one cabinet), or in areas where line-extenders were used in the HFC build (cables split in underground chambers). It can also be used to split the distribution to several smaller cabinets.

Your local Council should have asked for permission to install the cabinet there. Had they a formal record of your planting plans? If not it will have been a case of first come first served.

But it looks like there is still room for some shrubs, they will help to conceal the cabinet. 

The cabinet next to the old looks like an L4 distribution cabinet for the fibre drops to premises, and there are several of those connected to an upstream L3 aggregration cabinet. Over a long period of time, by which I mean up to around 2040, VM will eventually migrate everyone on the HFC network to fibre and in the process remove the coaxial cabling and old cabinets.

Thank you @nodrogd - I forgot they increased the density of the cabinets and the FB2s are equivalent of older build SD1i for distribution.

The one on its own is an SD1i cabinet. This will pass up to 96 homes directly, which is a bad number, or can be used to aggregate connections from 8 other cabinets. The other is a 64 homes passed FB2. The SD1i is probably taking in connections from the nearby FB2 and others and is going there as it's nicely out of the way, given it's not obstructing pavement and looks as though it's relatively out of sight. It had to go somewhere in the area and happened to be there.

The FB2 is to take the place of the part of the old cabinet customers would've directly connected to, the SD1i is to take the place of some other kit in the older cabinet that may have helped aggregate connections from other cabinets if you like.

Seems to be another chamber cover pretty close to the new one VM put in to serve the SD1i so shouldn't have lost much ground to replant.

Good luck with the community replanting: make sure the council are on board and leave the land alone, it is theirs to maintain. Have been involved in such a scheme myself and communication with the council throughout, especially their teams maintaining verges, was essential.