I'm now, thank goodness, teaching a straight year 1 class rather than a 1/2 mix so I don't have to worry about this this year. But I went to Maths moderation under the old testing regime a couple of years ago and yes, we did all have to take Maths books to share and agree level judgements. (The overwhelming conclusion was that it was very hard to say a child was working at level 3 based on book evidence alone as so much of their mathematical ability is shown through what they say, how they reason, the strategies they select etc.)
I wholeheartedly agree that KS1 Maths should be very practical but in this day and age you have to have evidence of what you've been doing. I absolutely refuse to stick photos into individual children's books as evidence of a practical lesson - life is too short. So I have a whole class scrapbook into which I stick a few photographs of each practical lesson, annotated with the date, objective and brief description of what was learnt. As long as I don't let it go longer than a week between uploading and printing out the photos, it's very manageable.
I will also often spread a lesson over two days, so on day 1 my input is followed by a practical activity which I photograph and sometimes the children choose to record in their Maths journals in their own way. On day 2 I'll repeat my input (adapted and abridged depending on what happened yesterday) and they will do some kind of written recording. That way I get the best of both worlds - they have the practical experience but also are learning to respond to written questions and I have evidence in the books of what they have learnt.
You have my every sympathy trying to manage an R/1/2 mix in one class - 1/2 nearly finished me off as it was so difficult to meet the needs of the children and teach in the way we are now required to, producing the required evidence of what had been going on. But I'm very surprised that your SLT haven't been asking for more written evidence of your Maths, definitely for year 2 and from now on, increasingly for year 1. Don't forget, your year 2s won't be able to use any practical equipment when they do their test so if you don't start to gradually reduce the practical activities and increase the amount of written work, they are going to really struggle with the test.