Royston is not needed, because it's covered on Cambridge lower part screen 5.
You will not be able to chain Peterborough and Cambridge directly, because there's a few boxes between.
Pitty Slough New is a IECC, otherwise it could be Peterborough+Cambridge+King's Cross+NLL+(Slough New)+(Reading)+Westbury+Didcot+Swindon+Bristol+Exeter.