Bus Train Pass combo for England?

https://www.nationalrail.co.uk/times_fares/ticket_types/plusbus.aspx

National Express isn't a bus company in the same sense as buses that serve a certain city or district. National Express are what are termed coaches in the UK and they're a national company that typically service long distance routes, think Greyhound buses in the US.

It’s a complex picture with a big coach company (National Express) serving city-to-City long distance routes and a hodge podge of multiple smaller bus companies so no, there’s no one rail/bus pass.

If you buy point-to-point train tickets you will sometimes be offered the chance to buy a thing called Plusbus, but I’m not sure what this is.

For National Express long distance buses, known as coaches, buy your ticket in advance.

On shorter bus routes, you will generally need cash - or a contactless debit or credit card in bigger cities. In London, only contactless or Oyster cards are allowed.

I doubt that any local bus would have the facility to deal with a credit card that isn’t contactless although I’m willing to be proved wrong.

For trains - www.nationalrail.co.uk
If going on a longer distance train journey of say over 1 hour, it is usually cheaper to pre-purchase tickets for specific trains in advance with the cheapest fares being loaded around 11 weeks ahead. On some routes, it pays top split the ticket - see www.trainsplit.co.uk

As has been said, National Express is more like Greyhound. Another company called Megabus is in competition for longer distance journeys.

The Plusbus that can be added to train tickets gives travel on most local buses at the destination. However, for most local buses you just show up at the bus stop, hold out your arm as the desired bus approaches and pay the driver cash - except in London where cards are needed. Some bus companies do not give change.
www.traveline.info is an excellent site for finding buses - but also includes trains.

Here is a site that explains about local buses in The Cotswolds:>http://www.cotswoldsaonb.org.uk/visiting-and-exploring/cotswolds-train-station/discoverer-one-day-pass/
(Moreton-in-Marsh is the rail station that most people travelling from London would use for this area).

Local buses, though not all, increasingly accept payment by contactless credit or debit card. Tickets are bought from the driver on the day.

The first step is to find out about buses in an area. For example, details for Cambridge can be found here:

https://www.cambridgeshire.gov.uk/residents/travel-roads-and-parking/buses/bus-timetables/

For Norfolk https://www.norfolk.gov.uk/roads-and-transport/public-transport/buses/bus-timetables-and-operators

Then you need to go to the bus operators’ websites and find out about day passes.

Traveline is a good site for journey planning

https://www.traveline.info/

Some of the bigger metropolitan areas such as Manchester have day passes available that cover most local trains, buses and trams. In the UK, the various train areas are operated by different companies and in many towns, there are multiple different bus companies, so if a place does offer a local day pass, check which companies participate in such a scheme, as the route you want may or may not be included.

Best to work on the assumption that they take cash not cards (the opposite is true for London!)

Also, if you have to pay cash on a local bus, make sure you have change. Most bus drivers will not be happy to change a £5 note, let alone a bigger one. A very few companies may still engage in the primitive and passenger-hostile practice of demanding exact fares in cash and not giving change at all.

Thank you all! This is really helpful!

Most bus drivers will not be happy to change a £5 note,

Outside London you might get a shock at ticket prices - a 15-minute journey can easily cost £3 upwards.

BritRail Passes don't offer any bus coverage, except for two Scotland-specific versions that do covers some coaches and ferries.

There are some regional schemes, some actually quite covering a wide area, such as The Great West Way. These don't cover every bus service but usually use specific ones to cover areas not covered by the rail part of the scheme. Don't know of any out East though.

I'd also add, for the sake of your own sanity, don't travel by bus during the school run hours. Stick to the times when the buses are primarily occupied by the elderly. The UK is not like the US where school buses are provided solely for pupil's transportation, most school kids, if they travel by bus, do so on public buses.