Thank you for getting back to us. I can understand why your trainer has given this advice. The review of Bakers Adult dry food is here
and as you can see, it has a nutritional rating of just 19%.
As your dog is quite young, it might be helpful to learn something about what to look for in a good dog food. There is a lot of information on this website and we have a thread here
which might help.
You can source a suitable dry dog food by using the Dog Food Directory.
As a start, maybe try these filters. You can adjust them yourself if you wish:
Type of food - dry, all.
Food properties - clearly labelled, certified nutritionally complete.
Rating - 60% to 100%
Avoid ingredients - all red, all yellow.
I have just tried this and it returned 12 pages. Unfortunately I cannot reproduce them here so you will need to do this yourself. Increasing the ratings slider to 75%-100% will reduce the list.
As you are on a budget, I would suggest that you have a look at Markus Muhle NaturNah which is available on Zooplus and Bitiba. It is a good quality, low priced food. The reviews are good. This is a cold pressed product and is different to the kibble that you are used to. It is dense and therefore you must weigh it at first to make sure you feed the correct amount. It is extremely easy to overfeed this product. Look on the Guru Pet Food website for specific instructions, also check out our thread on cold pressed foods here.
If you go for one of the cold pressed products they can be cost effective because you don't need to feed as much.
Whichever product you choose, remember to transition gradually to the new food so that your pup doesn't have any problems. Moving from a low quality food to a higher one can be a challenge so take it steady. These products are generic so you will not have to change the food again as your dog gets older.
If your budget can run to a giving fresh food on some occasions, there are benefits to the dog. Take a look at the thread Enhancement of dry dog food.
On the issue of behaviour and separation anxiety I can't really help. You are doing the right thing by following the instructions of your trainer. Patterdales are lovely dogs but can be hard work, as can other types of terriers. If you put the ground work in now you will hopefully have a nice, well behaved dog in time. He is still very young so remember not to over exercise him to protect his joints. People sometimes do this in the hope that it will tire the dog out and it will sleep. Rest is important and over stimulation can make them worse. This is particularly important where there are young children in the house.