There are many Underground Mathematics Resource Types. I do like the Review Questions which in the words of the Underground Maths Team:
These are questions designed to test students’ understanding of one or more topics and to exercise their problem-solving skills. In many cases they can also be used as a classroom resource to help teach concepts and methods. They are mostly drawn from past examination questions and have been chosen as ones that are interesting in nature and require non-routine thinking. The hints and solutions are designed to explain the reasoning and highlight connections as well as giving the answer. In many cases, alternative methods or solutions are presented.
Read about the use of Review questions in the classroom on this Teacher Support page. The fact that these questions are designed to test understanding of one or more topics, exercise problem-solving and proof skills and help students make connections make them ideal for use in the A Level classroom. They can be used to introduce a topic or are also ideal for review, something which should be a regular part of linear courses.
You can browse all the Review questions or narrow your search by question type; note the O/AO-level questions which are questions from old papers. One can also search by line (Number, Geometry, Algebra, Functions or Calculus) and by Station.
The Underground Maths team put together a spreadsheet that offers resource suggestions for each of the content statements in the DfE specification. Scroll down the page for the spreadsheet.
For each content statement, Underground Maths have suggested up to three rich resources and up to three Review questions. Each suggestion is hyperlinked to take you directly to the resource on the Underground Mathematics site. Resources that are particularly good at supporting the overarching theme of Mathematical modelling have been highlighted.
I have used many of the Review Questions successfully, something I will continue to do. My spreadsheet here gives the review questions by title rather than just number for each section of the subject contents. My starting point is the suggested review questions, most of which I have included; these are personal favourites. I can later add any additional suggestions.
The latest copy of the spreadsheet on this page on Underground Maths which is one of a series of pages on A Level Teaching Resources.