There are several version and denomination for a basic income. In this question, I will call unconditional basic income the situation were all citizens of a country receive regularly a lump-sum of money, independently of their age, their employment status and job,etc. I will assume that, at the moment the basic income is instituted, it is larger than the poverty threshold. I am also assuming that the basic income is not a substitute of other welfare subsidies.
The concept is gaining popularity these days, and for many reasons, economical or philosophical.
My understanding of offer and demand is that, if people can pay more for a product and are willing to do so, then prices will increase. So, it seems that, after the introduction of the basic income, there will be mechanically a large inflation. In a short time, people with no job and that relied mostly on the welfare system will be poor again. Worse, people with low income will be closer to the new poverty threshold.
1) What natural mechanical effects prevent an over-inflation after the introduction of a substantial basic income? By natural, I mean any direct or indirect effects of the sole introduction of the basic income.
2) If an inflation cannot naturally be avoided, what measures are usually suggested together with the introduction of the basic income?
Edit: my question is close but not an exact duplicate of this question. In the example of the other question, $A$ would receive $30$ and $B$ would receive $90$ for an unconditional basic income of $30$. If the two questions are equivalent, please explain.