I'm trying to talk in general here
The issue is that whilst low demand can cause low inflation, as soon as you're below 0 you run into major issues - that's unfortunately where we've just reached.
So long as the BoE keeps interest low people should be incentivised to spend their money as it's cheap to borrow; we haven't yet reached the stage where negative interest would be necessary, at which point you disincentivise the banks to lend, which is an entirely different problem (but arguably even more serious).
So if anything, if the government were faking this they'd fake low (but not very low) inflation as that's optimum - the problem with this is that all those independent economic groups who also do measures would be quick to call you out. Even aside from the central bank and the economy as a whole, there is a *lot* of money to be made from currencies as they increase/decrease in value against each other, and if the value of your currency was seen to be falsely inflated/deflated by false reporting the value of your currency would swing back to its actual value very quickly as demand/supply from currency arbitrageurs* would force this; the resultant shockwave would be far more serious than any gradual change, and the government would be very likely to be found out anyway, making this a very serious risk.
*basically, people who trade in different currencies to try and make money from their changing values relative to each other - sounds useless, but is actually the demand and supply that forces currencies to be at their correct value. They would be extremely quick to jump on any currency that was valued wrongly on purpose, either quickly selling to reduce its value proportionately or vice-versa.