The first bus on the left is the electrically driven Seddon Pennine RU, designated Silent Rider and numbered EX61 and originally with SELNEC PTE. It's apparently since been dismantled, but its sister car EX62 is now part of the museum collection. Wikipedia has this to say about the bus:
'The Seddon Pennine RU (for rear-underfloor, the location of the engine) was launched in 1969 as a competitor in the market for rear-engine single deckers. Although a very different product to the Pennine 4 it followed the same market-driven philosophy. Viz: offer the same major features as the most in-demand model but cut out most of the complexity, some of the purchase price and offer it for sale quickly and cheaply with the choice of in-house Pennine Coachcraft bodywork. The market leader was in the rear-engine single-deck segment was the Bristol RE and Seddon decided to use similar mechanical units, notably Gardner engines and Self-Changing Gears semi-automatic transmission.
The final RU to be delivered to a new customer was equipped with a Chloride sponsored battery-electric driveline and was called the "Silent Rider". It was sold to SELNEC (later Greater Manchester) PTE who numbered it EX61 in its experimental series, registering it XVU387M. The Chloride battery pack weighed four tonnes and the vehicle (unladen but for those batteries) weighed 13 tonnes (almost double the unladen weight of the Gardner-powered version) so payload was limited, by the axles fitted, to one tonne which equalled a capacity of B41D + 9 standing and although it featured regenerative braking the bus (like Lucas battery-electric Seddon Midi EX62 XVU364M which followed in 1975) was not a success. The Silent Rider project alone cost £100,000 at mid-1970s values, promotional tours to Sheffield and Chicago, Illinois, USA may have been prestigious for the Executive and for the manufacturers of vehicle and batteries, who were both major employers of voters in the PTE area, but Cook County Transit and the South Yorkshire PTE were, lacking the electrical-charging and cell-care infrastructure installed in a Manchester garage as part of the project, able to get even less use out of the thing than Greater Manchester who tried to employ its advertised 100-mile range by using it sporadically on one morning and one afternoon peak-time journey on routes 202/3. It was out of service by 1976.'
The next bus is a 1963 Daimler CVG6K with a Metro Cammell H37/28R body that was originally in service with Manchester City Transport, and the vehicle on the right is a 1939 Bristol K5G with a Willowbrook L27/24R body that was fitted in 1951 and was originally part of the North Western Road Car Company's fleet.