Recourse if heir (assuming to be only heir) gives away items intended for other heir before the content of the will is known?

Question

Please note that this matter was settled to my satisfaction. I have no intention whatsoever to make an issue out of it.
I’m asking the question mainly to satisfy my curiosity about what might have happened.

TL;DR below.

The full story:
In the spring of 2019 my close friend Peter, went out on a Friday night to get fish & chips, was run over by a drunk driver and he died on the spot.
His only next of kin was his mother Carla. She assumed she was the only heir.
Peter was an avid collector of SciFi and Fantasy books (same as me) and had approx. 6000 books in his apartment in Edinburgh.
Not knowing what to do with that enormous amount of books Carla called a local charity that runs thrift shops and offered them the books as donation. They send a guy over and he took away about 500 books. He promised to come back a week later with a larger van and more people to carry.

I flew to Scotland for the funeral (I live in The Netherlands) and to assist Carla in dealing with the situation.
That is when I learned she had given away those books. I explained to her that those particular books were not very valuable and giving them away was probably the best thing to do, but I knew that the entire collection was insured for £ 100.000 and that was most likely under valued.
Give it all away seemed silly. She agreed and we notified the charity to put the collection on hold.

Two days later Peters will was read. Turned out he was far wealthier than Carla or I knew. (We expected a few 100.000, but well over 10 million is a whole different game.)
He bequeathed a substantial amount to a few charities and had made sure that Carla would never have to worry about money for the rest of her live.
And he granted me his entire book collection plus an amount of money to cover my expenses for travel and dealing with the books (storage and shipping).

Carla was very upset she had given "my" books away.
I re-assured her that I didn’t mind at all.
I would have given them away myself as that made far more sense for these books than shipping them to my home in The Netherlands.

Over the following months I flew back and forth several times to further assist Carla and to deal with the books.
Eventually I shipped about 2000 books home and integrated them into my own collection. About 2000 where sold to a trader in second hand books and the remaining 1500 were donated to charity as Carla had done with the first batch of 500.
The proceeds of the sale and the remainder of Peters financial grant to me I donated in his name to the same charities that Peter had named in his will.

TL;DR:
An heir, assuming to be the only heir of the deceased, gives away part of his possessions prior to the content of the will being known.
What recourse does the other heir, to who those items were granted in the will, have if this can not be amicably settled?

Jurisdiction is UK, Scotland in case that matters.
Financial value of the items approx £200 to £250.
Presume that the items themselves can’t be retrieved anymore.

Answer 1

I think the key word here is "assume". A person, N, who is clearly the next of kin of a recently deceased person D may not assume that s/he is D's sole heir, or indeed is D's heir at all. N must wait until D's will (if any) is known, and an executor or administrator is lawfully appointed.

Only the executor may lawfully dispose of D's property, by conveying it to specified beneficiaries, selling it, giving it away, or by any other means. Anyone who does so without the proper executor's authority is probably technically guilty of theft, although in a case like the one in the question, a prosecution would be very unlikely.

But N would be liable to any heir H for the value of items properly left to H but disposed of by N. H might not choose to pursue such a claim, but would be legally able to. N should remember that the value, monetary or sentimental, of objects may not be known to N, and may be much greater to H than N is aware of.

I suppose that in the case of objects of slight value which must be dealt with promptly, such as perishable food on D's premises, reasonable steps would not be objected to.