Last week engineering work started. This is feasibility work, looking at whether the the proposed tunnel through Windsor can be built at a reasonable cost. It is being done by one of the largest and most respected rail engineering firms in the country. Once this is complete, the next step will be to do initial demand modelling to verify that there is an adequate business case, both for private investors and for Department for Transport.
Initial indications are that the engineering will be cheaper than initially thought but we’ll have a clearer idea when some initial drawings have been completed.