Etymology: Isengard and Helms Deep

[Rune Son of Bjarne]

Rather infuriating a Danish radioshow have been spreading the word that Tolkien was inspired by easter Jutland when coming up for place names, but offer little in the way of proof.

The very concept of the show is that a caller will make an unsubstantiated claim, and then the show will attempt to confirm or debunk the claim.

In this case the claim is that the place names Helm's Deep and Isengard comes from easter Jutland where you will find the narrow strait Hjelm Dyb and the manor house Isgård.

The consensus seemed to be that this must be coincidence, until a self proclaimed Tolkien ekspert calls in and claims that it is very likely that Tolkien got inspired by the Danish place names as he studied that area extensively. He offers no more detail, but starts talking about Tolkien's correspondence with the future Queen Margrethe II.

As a Danish Tolkien nerd this have left me perplexed. I haven't heard that Tolkien should have dedicated time to studying eastern Jutland, besides his general interest in the nordic countries.

Obviously Tolkien could have been inspired, and then altered the name to better fit in with old english, but it doesn't seem likely, does it?

What do you think?

Have you ever heard about Tolkien having a special interest in eastern Jutland (more specifically Djurs), or have you perhaps come across the origins of these place names.

As a bonus I just found a comment on reddit where a user suggest that the nearby village of Eskerod, could be the inspiration of Esgaroth.