grammar - Reported speech - "last January"

How would you change the time expression in the following sentence into a reported-speech form?
"We have not been to London since last January?"

What about "the last January?" Or, is there no change?

Answer

Next Month Jan 2019 we can say for Jan 2018

"We have not been to London since last January."

This current year (2018) we would not use last

"We have not been to London since January."

for Last year (2017)

"We have not been to London since January last."

The implication is January in the last calendar year.

In all cases if there is any question of doubt it is easier to say the year.