I am worried about going over the vat threshold and would like a filter in the income section for "last 12 months" is there one available?

I'll share some insight on your concern about reaching the VAT threshold in QuickBooks Online (QBO), @PJ UK.

If you mean the All Sales tab as the income section, select the Custom filter for the Date drop-down menu. Proceed to enter the date range you want on the To and From boxes.

Another option I can suggest is to run the VAT Liability report. It lists transactions that are in each box on the VAT return. This way, you can check if you're over the VAT threshold. To open this report, follow these steps:

1. Go to the Reports tab.
2. Search for VAT Liability report.
3. Edit the Report period to what you need, then press Run report.

I suggest you refer to this article to calculate VAT taxable turnover. It lists things you need to check if you've gone over the threshold in any given 12-month period. 

Tag me in a comment below if you have other questions about VAT in QBO. I'll be around to help you out. Have a nice day!