Apart from the previously advised London Paddington closures there will be the following major work-
London Liverpool Street (main line)- total closure 25 December to 2 January. All services (including) Stansted Express will start/terminate at Stratford. London Overground will use London Fields station as it's terminus.
In many cases Tottenham Hale or Seven Sisters on the Victoria Line will be the best tube interchange.
Cambridge- 24 December to 6 January- no trains at all from the London direction due to construction of Cambridge South. Rail replacement buses from Royston and Audley End
All Avanti West Coast and London North Western services (except to Birmingham) 25 December to 3 January disrupted or retimed due to major work at Crewe with no direct Liverpool trains and fewer Manchester trains. On 27 December no trains at all will run through Crewe (diverted via Manchester).
London St Pancras 21 to 29 December closed entirely for East Midlands and Thameslink trains. No service south of Bedford and Harpenden respectively. Bus replacements to outer London Underground stations and the East Coast Main Line.