Buy-to-let Inflation Affect on House Prices

There is no shortage of statistics on the rate of growth in house prices. The Nationwide has plotted them going right back to 1952:

House price inflation was discussed earlier in the section looking at Capital Growth. It is examined in more detail in Economics of Home Ownership.
Without expectations of capital growth few people would be interested in investing in buy-to-let. The gains to be made will be affected by capital gains tax.

We know the rates at which that is charged now, but these might well change by the time the property is sold, which could be many years in the future.
Government policy has sought to stabilise house prices, and reduce the speculative element in the housing market. Their efforts have been largely unsuccessful. Taxes on the speculative gains are one of the ways they might seek to influence this. Another might be the introduction of property taxes.

Rather than rely on a best guess at the rate of increase in house prices, financial modelling should be used to assess the level of increase that would be necessary to make the investment profitable, and then consider how likely that was.