Advice Best Itinerary for a Summer Trip to England?

My wife and I are planning a trip to the UK this summer and would like some advice/ideas for our itinerary. We're thinking of spending about 10 days in England, focusing on a mix of historical sites, countryside, and maybe a couple of days in London. What are the must-visit places that we shouldn't miss? Also, any tips on getting around or hidden gems that are off the beaten path would be greatly appreciated. Looking forward to your suggestions!