The short answer is yes, but it is more complicated (and therefore likely to be more expensive) than doing so before probate has been granted.
Once probate has been granted, the personal representatives can begin distributing the estate. At this point, it is likely to be harder to recover estate assets to settle any claim as they may have been sold or spent.
Before probate has been granted, you can protect your position by entering a caveat at the Probate Registry to prevent the executors obtaining a grant of probate and distributing the estate. This gives you time to prepare your claim and put forward your strongest position.
If it’s not possible to contest a will before probate is granted, it is still better to act quickly. As soon as you become aware of your potential claim, you should take steps to establish the grounds for your claim, gather the available evidence and notify the personal representatives.
If making a 1975 Act claim, remember that you only have six months from the date the Grant of Probate is obtained to issue your claim.
Getting expert advice early on can help you avoid the pitfalls of contesting a will after probate has been granted.