Wall Ties in 1920 built house

[JezJez]

Hi, I'm re-pointing the front of my house which was built in or around 1920.
It has a cavity wall build, inner wall is of yellow brick, outer wall is very hard red brick. The cavity seems quite small 50mm and has been cavity wall filled (I would say a long time ago). My question is this, do I need to replace the wall ties, if yes, is it easy considering that the cavity is filled?

Thanks for any advise that comes my way
Jez

 

[Bosswhite]

Its a specialist job, Building Societies tend to make this a condition these days on older properties when applying for a mortgage