Hi,
Once a trust becomes liable to tax, the trust must be registered with HMRC and a tax return submitted each year.
We cannot advise on the type of trust or whether it has become liable to tax on this forum. You can see guidance on trusts and taxes here:
Trusts and taxes
Trustees - tax responsibilities
You do not have employ the services of an accountant to submit a SA900 or SA905 for the trust. The trustees can submit the tax return themselves. Where there are 2 or more trustees, they nominate a 'principle acting trustee', who will submit tax returns either on paper or online, on behalf of the trust.
Thank you.